doc: update 4.0.4 entry
doc ja: translate
Bump version
doc: add cross-compile document

How to cross compile for Rroonga under Debian like environment.
doc cross-compile: Ruby 1.9.3 bundled rubygems needs update
doc cross-compile: remove needless command
test: update inspection of Groonga::Expression

update inspection result of grn_expr for Groonga 4.0.5.
It changed: `\"\" -> null`