Merge pull request #209 from diegocaro/master

Adding target_include_directories directive to auto include headers
removed googletest and added submodule instead
init googletest submodule in install.sh
make tests point to the new header location
only grab google test if running the tests
Merge pull request #211 from mpetri/master

Remove googletest sources from repository and use submodule instead
Fix for issue #210

char2comp now checks if the character is in the alphabet.
The std:: namespace prefix was also added in the io.hpp
for stoull (see issue #212).
Merge pull request #213 from simongog/fix_210

Fix for issue #210