Rename included files with underscores

`all.scss` correctly references variables and 
other dependencies, however middleman was trying 
to produce css versions of all files but could not
because stand alone files did not reference 
variables and others as in `all.scss`.

Prefixing with underscores means stand alone files
are not created!
Normalize is already referenced inside all
Merge pull request #4 from kaichanvong/master

Fix compiling woes