Excludes external libraries from code coverage

They provide far more code than we actually use.
And we certainly don't want to test all that code!

.travis.yml

@@ -25,7 +25,7 @@ install:
 
 after_success:
   # exclude some directories from profiling (.libs is from autotools)
-  - export EXCLUDE_COVERAGE="--exclude sassc --exclude sass-spec --exclude .libs"
+  - export EXCLUDE_COVERAGE="-e sassc -e sass-spec -e .libs -E json.* -e debug.hpp -e cencode.c -e b64 -e utf8 -E utf8.* -E utf8_string.* -e test"
   # debug via gcovr
   - gcovr -r .
   # debug via coveralls (dump result for futher analyzing)