Support SQLite in a statically-linked binary

Follow up to #136 (closed).

Contrary to what's mentioned in #136 (closed), it turns out it's possible to build a statically-linked Comentario that supports SQLite. For Alpine, it requires the following env. variables set:

- CGO_ENABLED=1
- CC=musl-gcc
- CGO_LDFLAGS=-static

And, apparently, the presence of musl-gcc.