Add grunt-contrib-htmlmin.
Merge pull request #25 from mpc-hc/htmlmin

Add grunt-contrib-htmlmin.
Tweak the sprite; add margin to avoid overlapping.

I noticed this on mobile when zooming.

Command used (for future reference):

`>glue images sprites --margin=10 -a vertical --html`
trac.rb: Improve regex.
downloads.md: fix link to file.
Add a news about Transifex