Log Message:
Update to 0.5.6:

0.5.5 -> 0.5.6
=================
Akira TAGOH (1):
      Fix distcheck error

David Tardon (2):
      install lt-config.h: it's included from langtag.h
      remove stray LT_END_DECLS

0.5.4 -> 0.5.5
=================
Akira TAGOH (6):
      Fix a memory leak
      Fix a typo
      Fix configure error on specifying --disable-modules
      Fix a build issue with inline keyword
      Fix warning on bootstrap
      Update revision