Merge pull request #28 from l/translation_ja

core: update Japanese translations
doc: update Japanese auto-generated files
core: add key alt-j,alt-f to jump to first buffer, change command for jump to last buffer

New key alt-j,alt-f is bound by default to "/buffer -".
The existing key alt-j,alt-l is now bound by default to "/buffer +".
core: fix use of reserved C identifiers in headers (closes #31)
irc: add command /allpv (task #13111)
irc: fix typo in /help allpv
core: fix add of filter on OS X when regex for message is empty (filter regex ending with "\t")
core: update German translations
doc: update German auto-generated files
api: add support of nested variables in function string_eval_expression and command /eval (closes #35)
doc: add plugins trigger/exec in CMake options and list of default plugins (user's guide)
doc: update list of actions executed when a trigger is called (user's guide)
doc: update question about messages displayed on channel join (FAQ)
core: fix typo in /help command
irc: add command /unquiet (closes #36)
irc: update description of some commands
irc: fix arguments in /help unquiet: at least one nick/host is required
irc: replace "user" by "nick" in description of commands
doc: replace "echo -e" with "printf" in user's guide
Contributing.asciidoc: fix developer's guide link

The link directed to WeeChat.org instead of the developer's guide.