Check-in the initial libpycr sources

Adds the following to the repository:

    - libpycr sources under /libpycr
    - cl executable script under /scripts
    - setup.py to install the pycr module using Python's setuptools
Add LIST command.

Lists the changes with given STATUS and OWNER.
Defaults to list OPENed changes for owner SELF.
Remove the --no-color and disable color by default

Use the core.color configuration attribute to turn colored output on. It
accepts any supported Pygments formatter name as value, as well as the
special value "auto".
Fix the command-line help

Disable automatic handling of sub-commands "--help" option and handle it
manually.

Also add a check for LIST command's --status argument value to prevent
making a wrong request to the server.
Re-write configuration management.

config.Config object is now the holder of all the configuration. Every
module in the project should refer to it to store or fetch there
configuration value.
Add support for pager and editor.

Use the pager for both the SHOW and LIST command.
The pager can be set for all commands via the core.pager configuration
option. It can also be set per-command via the pager.<command> options.
Setting pager.<command> to the empty value will disable the pager for
that command. Setting core.pager to the empty value will disable the
pager for every commands.
Add the patch to the output of SHOW

Update the formatter and default styles.
Optimize requests made to the server.

Use a Session to keep connection open and reuse them when multiple
requests.
Build the token list and then format it

This avoid having multiple print statements, and keep the output more
consistent on error.
Implement the REBASE command.

Also refactor the libpycr.gerrit module and moves all Gerrit internal
structures definition to libpycr.struct module.

Fix an issue with base64 decoding (when padding == 3).
Update output of all commands

Tokenize all output and format it with pygments. This allows a
consistent use of the tokenization mechanism and ensures a consistent
output of structures across all commands.
Add defaults to LIST command usage.
Update REBASE output (display diff).
Endpoints are now computed by the Api class.
Implement the SUBMIT command.
Implement the REVIEW command.