chore(cmake): use find_packages after setting CMAKE_MODULE_PATH
chore(.travis.osx.yml): update gcc version, fix package install
chore(.travis.tml): Removed tools/proof-checker
fix(shell/parser/parser_2): Add defines tag
fix(.travis.osx.yml): typo
Merge pull request #3 from JichaoS/master

style(shell/*): Fix comments
feat(shell): partial support for bison
chore(.travis.osx.yml): fix typo
chore(.travis.osx.yml): add brew upgrade
fix(*): Added dependencies and fixed flex

The macro ${FLEX_EXECUTABLE} must be within parenthesis to compile for
some reason.

Bison 2.7, Flex 2.5.35, Cmake 2.8.12.2
fix(*): Added quotes to ${BISON_EXEC}
fix(src/*): Added sys-independent FlexLexer.h
fix(test/types/formula/CMake): Added threads
fix(test/types/formula/CMake): Added threads
fix(CMakeList.txt): Add sub-dir after packages
feat(shell/CMakeLists.txt): Multi-platform Support

Now we require Bison-2.3 and above, and Flex 2.5.35 and above.

For OSX we use FlexLexer_osx.h instead due to header incompatibility
issues[1]

[1] https://bugs.launchpad.net/zorba/+bug/1034582
fix(shell/CMakeLists.txt): Include bison 2.3
fix(shell/scanner.h): Scan for FlexLexer locally
chore(CMakeLists.txt): No FlexLexer style-check
style(*): fix