Remove _config.yml from .gitignore.
Remove useless excludes from _config.yml.

Custom builds worked by accident since that exclude didn't take effect due to Jekyll's issues with excludes.
Losslessly compress PNG files.

Before: 16,4 MB (17.219.668 bytes)
After:  15,6 MB (16.460.240 bytes)
Merge pull request #39 from XhmikosR/gh-pages

Minor tweaks