debian: link against libgcrypt20-dev and libgnutls28-dev
doc: add missing file "tests.cpp" in developer's guide
tests: don't install binary "tests" with autotools
tests: add partial tests of functions hashtable_set*
tests: add tests of function string_split_shell
tests: fix memory leaks
tests: read WeeChat command line arguments in environment variable "WEECHAT_TESTS_ARGS"