This threads the original glob given by end users through all of the
glob parsing errors. This was slightly trickier than it might appear
because the gitignore implementation actually modifies the glob before
compiling it. So in order to get better glob error messages everywhere,
we need to track the original glob both in the glob parser and in the
higher-level abstractions in the `ignore` crate.
Fixes#444
This commit completes the initial move of glob matching to an external
crate, including fixing up cross platform support, polishing the
external crate for others to use and fixing a number of bugs in the
process.
Fixes#87, #127, #131
