Release v0.5.1

CHANGES:

- Fix invalid AST due to empty binding list in `ppx_regexp`.

Release v0.5.0

CHANGES:

- Migrate `ppx_regexp` to ppxlib.
- Change license exception for `ppx_regexp` to the LGPL-3.0 Linking
  Exception.

Distribution v0.4.3

Update changelog in preparation for v0.4.2.

Distribution v0.4.1

Distribution v0.4.0

Change jbuild libraries from re.pcre to re.perl.

Prepare change log for v0.3.1.

Add ppx_regexp.descr.

Merge remote-tracking branch 'origin/master' into ocaml-4.02