pool: handle server connection state

Add server state tracking to the pool connection. The connection Close
method clears watch and transaction state. If a subscription or monitor
command was used, the underlying connection is closed.

Fixes issue #53.
Update doc to new and improved Redis terminolgy
Improve pool documentation.
Improve pool documentation.
Fix typo in docs
Merge pull request #58 from wricardo/master

Fix typo in docs
Cleanup pub/sub state on pool close.
Rename DialTest to DialTestDB.

Also, add doc comments to the dial() and DialTestDB() functions.
Fix doc typo
Merge pull request #61 from kjk/patch-1

Fix doc typo
Remove line left from debugging session.
Fix punctuation in scan.go ScanStruct comment
Merge pull request #63 from tp/patch-1

Fix punctuation in scan.go ScanStruct comment
Refactor convert & assign code.

Add convertAssignValue and use everywhere that convertAssignInt and
cnvertAssignBytes are used.
Add benchmarks.
Optimize Do("")
Add Uint64 reply helper.
Clear redisx package.

The features were moved to the main package long ago.