[texdoc] Texdoc 3.1 has been released

[Takuto ASAKURA]

Hi All,

I've just uploaded Texdoc 3.1. The main changes are:

- New option -c: changing configure temporally
- New config item `texlive_tlpdb` to specify a path for texlive.tlpdb
- Fixed an issue that texdoc fails to open gzipped file in GNOME/XFCE
- Added prefixes to script files not to contaminate kpse search space
- Many other small improvements and bug fixes

There are only a few new features for the end-users, but the internal
implementation (more specifically, the entire module structure) has
been drastically changed. This is related to a request from Karl to
add prefixes to the script files. I checked several times, but there
is still a possibility that the changes will be a cause of unexpected
errors. I will appreciate if you could try and test this new version
during the pre-test period of TeX Live 2019.

Thanks,
Takuto