[release] update to version 1.2.1

[fantazio]

Ready for release : opam install . works as expected.
Upon approval of this PR, I'll publish the package on opam.

This release includes:

• Fix uncaught exception with anonymous submodules #84
• Do not create remove_bad_files.sh #86
• Extend module type related limitation #91
• Do not report elements of code defined in module types #92
• Improve incl_same_name #93
• [docs][methods] quick fix toc #94
• Collect exports directly from the Typedtree.structure on .cmt without .cmti #95
• Simplify and strenghten the representation of file infos #96
• Track type equivalences #97
• Track methods uses through object aliases #98
• Analyze more complex factory functions #99

Internal changes are:

• Some tests break with ppx_deriving.6.1.2 #87
• Add a few utils script #88
• [check][ref] some tests are fixed with ppx_deriving.6.1.3 #90

It is focused on bug fixes.
The following issues are fixed:

• Elements from external libraries may be reported #55
• Unexpected reported value included from a module type with substitution #64
• Methods uses are not tracked through object aliases #66
• Methods are not analyzed if a factory function's object is bound before returning #67
• Constructors uses are not tracked through type equations #79
• Fields uses are not tracked through type equations #80
• Fields and constructors uses are not tracked though module aliases #81
• Fields and constructors uses are not tracked through include #82
• Don't create remove_bad_files.sh #85

[nojb]

LGTM