bump library version to 1.3 since there are incompatibilities

The key/password API will break the old one, so at least bump the version.
add separate APIs for working with passwords and raw keys

If people are going to handle the password themselves, or for use as a FUSE
filesystem, then most likely, passwords will be the way to go.  For use in
IOCipher in conjunction with CacheWord, things work best if raw key data is
used.  That way CacheWord can pass the raw key data that it manages
directly to IOCipher.

fixes #3173 https://dev.guardianproject.info/issues/3173
tests: silence cppcheck unreadVariable and variableScope warnings

I have found that fixing the trivial warnings makes cppcheck more likely to
find real issues.