Client authentication improvements.

Makes SaneClientAuthentication implement SanePasswordProvider.

Adds a canAuthenticate(String) method to SanePasswordProvider.

Adds a String parameter to the getUsername and getPassword methods of
SanePasswordProvider.

Makes SaneClientAuthentication the default provider of authentication.

Code reformatting.
Update README.md for authentication
Fix unnecessary initialize and improve javadoc.
Merge branch 'master' of github.com:sjamesr/jfreesane
Add SaneRpcCode.

Adds SaneRpcCode, an enum representing all the RPCs available to the
client.

Uses SaneRpcCode where appropriate.
Update maven-release-version, update SCM paths
[maven-release-plugin] prepare release jfreesane-0.91
[maven-release-plugin] prepare for next development iteration
Fix deprecation warning.

Fix deprecation warning by simply propagating the IOException that gets thrown
by close().
Fix unused variable warning.

Rename a few variables so it's clearer what they are.
Fix formatting.
Extract a bunch of inner classes.
Remove unused logger
Point to release 0.91
More link updates
Reorder the ADF section of the readme
Fix order in the table of contents
Removed reference to deleted wiki page.