diff_output: remove unused parameter

Signed-off-by: schu <schu-github@schulog.org>

Adding multi-cpu compile option when generating MSVC projects.

Signed-off-by: schu <schu-github@schulog.org>

add chicken-git bindings to readme

Fix the build on Windows

write_section() mistakenly treated is input as the whole variable name
instead of simply the section (and possibly subsection) and would
confuse "section.subsection" as a section plus variable name and
produce a wrong section header.

Fix this and include a test for writing "section.subsection.var" and
reading it from the file.

Cleanups to the README

easier for the casual reader to find.

Rename git_oid_to_string to git_oid_tostr

To conform the naming scheme of git_oid_fromstr we should change the
name of git_oid_to_string to git_oid_tostr.

Since strnlen is not supported on all platforms and since we
now have the shiny new git_text_is_binary in the filtering
code, let's convert diff binary detection to use the new stuff.

To make this code more resilient to future changes, we'll
explicitly translate the libgit2 structure to the libxdiff
structure.

This should restore the ability to include libgit2 headers
in C++ projects.

Add specfile and packaging instruction for creating Fedora RPM

This reverts the changes to the GIT_STATUS constants and adds a
new enumeration to describe the type of change in a git_diff_delta.
I don't love this solution, but it should prevent strange errors
from occurring for now.  Eventually, I would like to unify the
various status constants, but it needs a larger plan and I just
wanted to eliminate this breakage quickly.

This clears up the memory leaks that valgrind seems to find on
my machine.

It turns out that commit 31e9cfc4cbcaf1b38cdd3dbe3282a8f57e5366a5
did not fix the GIT_USUSED behavior on all platforms.  This commit
walks through and really cleans things up more thoroughly, getting
rid of the unnecessary stuff.

To remove the use of some GIT_UNUSED, I ended up adding a couple
of new iterators for hashtables that allow you to iterator just
over keys or just over values.

In making this change, I found a bug in the clar tests (where we
were doing *count++ but meant to do (*count)++ to increment the
value).  I fixed that but then found the test failing because it
was not really using an empty repo.  So, I took some of the code
that I wrote for iterator testing and moved it to clar_helpers.c,
then made use of that to make it easier to open fixtures on a
per test basis even within a single test file.

This is a major reorganization of the diff code.  This changes
the diff functions to use the iterators for traversing the
content.  This allowed a lot of code to be simplified.  Also,
this moved the functions relating to outputting a diff into a
new file (diff_output.c).

This includes a number of other changes - adding utility
functions, extending iterators, etc. plus more tests for the
diff code.  This also takes the example diff.c program much
further in terms of emulating git-diff command line options.

Some changes that merged cleanly actually broke the unit
tests, so this fixes them.

This is an initial version of git_diff_workdir_to_index.  It
also includes renaming some structures and some refactoring
of the existing code so that it could be shared better with
the new function.

This is not complete since it needs a rebase to get some
new odb functions from the upstream branch.

Once I added tests for the whitespace handling options of
diff, I realized that there were some bugs.  This fixes
those and adds the new tests into the test suite.

* Implemented git_diff_index_to_tree
* Reworked git_diff_options structure to handle more options
* Made most of the options in git_diff_options actually work
* Reorganized code a bit to remove some redundancy
* Added option parsing to examples/diff.c to test most options

File mode flags are not all defined on WIN32, but since git
is so rigid in how it uses file modes, there is no reason not
to hard code a particular value.  Also, this is only used in
the git_diff_print_compact helper function, so it is really
really not important.

This fixes several bugs, updates tests and docs, eliminates the
FILE* assumption in favor of printing callbacks for the diff patch
formatter helpers, and adds a "diff" example function that can
perform a diff from the command line.

This reworks the diff API to separate the steps of producing
a diff descriptions from formatting the diff.  This will allow
us to share diff output code with the various diff creation
scenarios and will allow us to implement rename detection as
an optional pass that can be run on a diff list.

This gets the basic plumbing in place for git_diff_blob.
There is a known issue where additional parameters like
the number of lines of context to display on the diff
are not working correctly (which leads one of the new
unit tests to fail).

This cleans up the various GCC compiler warnings with the
xdiff code that was copied in.

Since casting to void works to eliminate errors with unused
parameters on all platforms, avoid the various special cases.
Over time, it will make sense to eliminate the GIT_UNUSED
macro completely and just have GIT_UNUSED_ARG.