- fix position modport-to-modport bindings
- inout logics converted to regs become outputs

Some .v files are incorrectly identified by GitHub Linguist as Coq or Vlang
files, which confuses people who browse the repo on GitHub. According to
https://github.com/github/linguist#using-gitattributes adding a .gitattributes
file can solve this problem.

- constant folding supports hex numbers
- simplify mod
- simplify pow
- elaborate !(a == b) into a != b

- made stream conversion pure
- type param conversion uses Set for instance uniqueness
- updated NOTICE and resolutions

- added Windows build
- separate build and test jobs
- per-OS release artifact generation

Without this patch, a stray `endif caused sv2v to take the tail of an
empty list. Now we raise a lexical error.

To do this, the patch pulls the "push" and "pop" logic for the
preprocessor condition stack into separate helper
functions (pushCondStack and popCondStack). It also defines some
helper functions for manipulating Cond's.

The patch also adds a documentation comment explaining what the
different values of Code meant (because I had to squint to work it
out).

Yosys does support some asserts nowadays. Allowing sv2v to not strip
them out means that you can check formal properties without needing
hierarchical references (which Yosys really doesn't cope well with!)