Add some missing comments.

ok @davecgh
Add vet and lint where possible to travis.
Error improvements for lint.

Rename errors to Err*.
Lowercase error text.

Add golint for top level package

ok @davecgh
Fix tests.
Update ldb tests for latest API error changes.
Changed TxIn.PreviousOutpoint to TxIn.PreviousOutPoint after btcwire API change.
Merge remote-tracking branch 'conformal/master' into confmerge

Conflicts:
	.travis.yml
Merge pull request #3 from mably/confmerge

ppc: merged conformal/master, tests ok