Avoid useless file write

Don't write .mustache file ( Close #2 ) & only write index.html if it
has change. It's better for watching process (eg: avoid useless
livereload).
Also fix test ( close #1 ) & add some options for the template index
filename & update the README according to that.

This commit remove wrench dependency ;)
Merge pull request #16 from MoOx/avoid-useless-write

Avoid useless file write