Cleaned up usekey support:
* documentation updated (for en; still must update for other languages)
* argument list no longer cares about position of flags relative to non-flag args
* encryption goes to stdout if no --destination specified
* encryption reads from --stdin if no [message] specified
This should address issues 100, 101, 102, 103.
Added test case for usekey command in KeyTool.
Quick lint audit to ensure I don't add to confusion. :)
Updated the docs to correctly state that usekey will also sign messages. Fixed a whitespace problem.
Session: Add encoder and decoder params to Encrypt() and Decrypt()

This makes the API match Crypter and Encrypter.

Signed-off-by: Devin Lundberg <dlundberg@google.com>
Added encoder options to api operations so base64 encoding and decoding can be turned off/modified
Fixed docs regarding signature formats
Added unit tests for encoding on signers.
Merge branch 'usekey-fixes'