This commit does the work to delete the old `grep` crate and effectively
rewrite most of ripgrep core to use the new libripgrep crates. The new
`grep` crate is now a facade that collects the various crates that make
up libripgrep.
The most complex part of ripgrep core is now arguably the translation
between command line parameters and the library options, which is
ultimately where we want to be.
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
