config: specify how we match the regular expressions

We do it the same as git does: case-sensitively on the normalized form of the
variable name.

While here also specify that we're case-sensitive on the values when handling
the values when setting or deleting multivars.

include/git2/config.h

@@ -398,6 +398,9 @@ GIT_EXTERN(int) git_config_get_string_buf(git_buf *out, const git_config *cfg, c
  *
  * The callback will be called on each variable found
  *
+ * The regular expression is applied case-sensitively on the normalized form of
+ * the variable name: the case-insensitive parts are lower-case.
+ *
  * @param cfg where to look for the variable
  * @param name the variable's name
  * @param regexp regular expression to filter which variables we're
@@ -410,6 +413,9 @@ GIT_EXTERN(int) git_config_get_multivar_foreach(const git_config *cfg, const cha
 /**
  * Get each value of a multivar
  *
+ * The regular expression is applied case-sensitively on the normalized form of
+ * the variable name: the case-insensitive parts are lower-case.
+ *
  * @param out pointer to store the iterator
  * @param cfg where to look for the variable
  * @param name the variable's name
@@ -487,6 +493,8 @@ GIT_EXTERN(int) git_config_set_string(git_config *cfg, const char *name, const c
 /**
  * Set a multivar in the local config file.
  *
+ * The regular expression is applied case-sensitively on the value.
+ *
  * @param cfg where to look for the variable
  * @param name the variable's name
  * @param regexp a regular expression to indicate which values to replace
@@ -506,6 +514,8 @@ GIT_EXTERN(int) git_config_delete_entry(git_config *cfg, const char *name);
 /**
  * Deletes one or several entries from a multivar in the local config file.
  *
+ * The regular expression is applied case-sensitively on the value.
+ *
  * @param cfg where to look for the variables
  * @param name the variable's name
  * @param regexp a regular expression to indicate which values to delete
@@ -552,6 +562,9 @@ GIT_EXTERN(int) git_config_iterator_new(git_config_iterator **out, const git_con
  * Use `git_config_next` to advance the iteration and
  * `git_config_iterator_free` when done.
  *
+ * The regular expression is applied case-sensitively on the normalized form of
+ * the variable name: the case-insensitive parts are lower-case.
+ *
  * @param out pointer to store the iterator
  * @param cfg where to ge the variables from
  * @param regexp regular expression to match the names
@@ -568,6 +581,9 @@ GIT_EXTERN(int) git_config_iterator_glob_new(git_config_iterator **out, const gi
  * The pointers passed to the callback are only valid as long as the
  * iteration is ongoing.
  *
+ * The regular expression is applied case-sensitively on the normalized form of
+ * the variable name: the case-insensitive parts are lower-case.
+ *
  * @param cfg where to get the variables from
  * @param regexp regular expression to match against config names
  * @param callback the function to call on each variable
@@ -693,6 +709,9 @@ GIT_EXTERN(int) git_config_parse_path(git_buf *out, const char *value);
  * This behaviors like `git_config_foreach_match` except instead of all config
  * entries it just enumerates through the given backend entry.
  *
+ * The regular expression is applied case-sensitively on the normalized form of
+ * the variable name: the case-insensitive parts are lower-case.
+ *
  * @param backend where to get the variables from
  * @param regexp regular expression to match against config names (can be NULL)
  * @param callback the function to call on each variable