C implementation of base64 encode/decode.

This started as a fork of the implementation Bob Trower produced and released in 2001. You can find the original here: http://base64.sourceforge.net/

As we started using the library we found it was hugely handy, but had a few bugs and not as many tests as we wanted. As the upstream project seems to have lost steam, we decided to fork, improve, release and ship.

meson setup --warnlevel 3 --werror build
cd build
ninja all test coverage
firefox meson-logs/coveragereport/index.html