build: Clean up the main Makefile.am
parser: Always use a valid GError internally

Do not just pass the GError through from the public-facing arguments: we
may want to perform error checking internally at any later date.
parser: Always perform UTF-8 validation

JSON is defined to be encoded using UTF-8, so we should not rely on
the documentation saying so when parsing, but validate the input and
eventually provide a recoverable parsing error.
Add validation tool

The json-glib-validate tool is a small utility that validates the data
found at the URIs passed on its command line.
Add format tool

A simple command line utility to format JSON data; it allows prettifying
and unprettifying JSON.
docs: Add infrastructure to build man pages

The small utilities we build and install should have their own manual
pages.
build: Clean up configure summary
Add abicheck.sh test output to the ignored files
po: Add utilities to the POTFILES

They come with translatable strings.
Updated Brazilian Portuguese translation
Improve consistency in error messages

Use the same spacing and formatting rules.
docs: Include tool man pages in the API reference

The small utilities we ship should have their main pages included in the
API reference, similarly to what GLib does.
Updated Spanish translation
Updated Galician translations