Bring in the errgo error type locally.
Unexport Err attributes and interfaces.
Mostly documenation clean up.
Rename and cleanup.
Moving code around
Don't forget this one.
More doc cleanup.
Store locations not line numbers.
Moving more tests around.
Remove unused callers.
Add missing headers and update the doc.
Test nil params, and skip deferred test with gccgo.
More nil checks.
Update the readme.