Compile-time translation of `{%trans%}` and `_(..)` by blocktrans_fun #131

So, to fully translate template to multiple languages, we need just
blocktrans_fun and blocktrans_locales in compile-time.
No need for gettext server in runtime, to translate `trans` and `_(..)`.
Don't distinguish trans and blocktrans in internal code; fix opts.

Append `locale` compile-time option value to `blocktrans_locales`.
Some docs updates.
Drop unnecessary 3'rd argument of `erlydtl_runtime:translate/3`
Fix #132 according to comments in that pull request.