tests: add -v option for command "tests" to increase verbosity (CMake)
tests: run tests after build on Travis CI
core: add option "--yes" for add-apt-repository (Travis CI)
core: download debian package libcpputest-dev from weechat.org (Travis CI)
core: check that string is not NULL in function string_input_for_buffer
tests: add tests of function string_is_word_char
core: check that from/to arguments are not NULL in base16/64 functions
tests: add tests of functions string_iconv*
tests: add tests of function string_format_size
irc: fix duplicate sender name in display of wallops (closes #142, closes #145)
tests: fix compilation of tests

The header gui-curses.h doesn't need to be included (this causes an error
because the real ncurses lib header is not found when compiling tests).
api: fix function string_format_size on 32-bit systems
core: replace package libcpputest-dev by amd64 version (Travis CI)
core: remove unused ubuntu PPA (Travis CI)
tests: remove test of han char in utf8_char_size_screen (failing on Ubuntu Precise)
tests: remove test of han char in utf8_strlen_screen (failing on Ubuntu Precise)
Merge branch 'travis-tests'
relay: fix number of bytes sent/received on 32-bit systems
trigger: fix hook count on 32-bit systems
api: fix function string_decode_base64

The result of function was sometimes wrong, for example base64 decoding of
"YWJj" was returning "ab" instead of "abc".