Fixed compatibility with Ruby 1.9
Fixed compatibility with Ruby 1.9

The regular expression syntax seems to be different in 1.9, causing
errors in the caps filter with the extended groups feature to
selectively turn case sensitivity on or off.

Now a syntax is used that seems to be compatible with both Ruby 1.8.x
and 1.9.x.

Closes #6.

avdgaag/typogruby