Move sexpr_funcs to sexpr_fn. Using consistent file name conventions.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Use fullpath in #include directives.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Rename lean frontend files. The prefix lean_ is not necessary anymore.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Update README.md

put http://build.leanprover.net
[skip ci]
Update .travis.yml

move triggers from 1st conf. to 4th conf to balance loads
[skip ci]
Use fullpath in #include directives, add missing STL headers
Use fullpath in #include directives, add missing STL headers