Removed distrubution of generated file liblouis.h.

Including this file in the distribution could generate a nasty bug
where the library would be built with conflicting definitions of
widechar. This bug only occurs when configuring in a subdirectory
instead of $top_srcdir.
Merge pull request #8 from IndexBraille/feature/fix-subdir-build

Removed distrubution of generated file liblouis.h.