Update asset pipeline and mailer md
some refinements on asoociation.
Update pg guide.
Update src.
New guide: 4.2 release notes.
Sync with src 42 release guide (zh_TW)
Finish translation of 4.2 release notes

Fixes #58
Hide Rails Nested Model Forms
trans command line (sip).
Update gettiong_started.md, cc #43.
Update pg guide, view => database view.
trans getting_started.md
Merge remote-tracking branch 'docrails-tw/master'
Update config.md
tans getting_started.md
Merge remote-tracking branch 'docrails-tw/master'