Update format_rsakey_from_pem() in keys.py.

Update repository_tool.py and keys.py functions that import rsa publickey files.  Perform a simple check of the PEM string so that an improperly formatted PEMis detected sooner.  Reported by Santiago.
Merge branch 'repository-tools' of https://github.com/theupdateframework/tuf into repository-tools
Raise exception if key not found in the key-removal methods.

Santiago's request:  The key-removal methods in repository_tool.py should raise an exception if the key argument has not been previously loaded.  They previously returned silently if the key was not found.
Update README.md

Fix write() parameter in the Consistent Snapshots section.
consistent_snapshots -> consistent_snapshot
Update README.md

Lines 204-213: Update comments for get_filepaths_in_directory() and add_targets() examples.
Modify load_signing_key() exception message.

The previous exception raised when a non-signing key is loaded may be misinterpreted:
tuf.Error: The private key is unavailable.

Changed to: This is not a private key.
Merge branch 'repository-tools' of https://github.com/theupdateframework/tuf into repository-tools
Update README.md

Add Table of Contents.
Add documentation for the Consistent Snapshots section.
Update repository_tool.py.

Properly strip (again) the digest prepended to 'digest.filename' files.
The required '+1' appears to have been accidentally deleted in a recent commit:
https://github.com/theupdateframework/tuf/commit/298f52ddb8a6c017e4892a2f1de6545f7715de59#diff-59d384d80d746c800b16c8387756c0ccL2750
Thanks to Santiago for locating the bug.
Merge branch 'repository-tools' of https://github.com/theupdateframework/tuf into repository-tools
Update modules reviewed by Monzur.

Update keys.py and pycrypto_keys.py following Monzur's code review.
Update affected modules.
Update README.md

Add purpose section header.
Consistent snapshot section: file attributes (archive, hidden, access?) -> file hash.
Update tuf-spec.txt

Address issue #179
Lines 800, 803: (root|timestamp).digest.json -> digest.(root|timestamp).json
Update repository_tool.py and util.py.

Rename the unused 'json_object' variable in util.py.

Roles are allowed to share verification keys.  Update repository_tool.py so that the targets role can successfully load an already recognized key when loading a repository.  Reported by Santiago.
Merge branch 'repository-tools' of https://github.com/theupdateframework/tuf into repository-tools
Log warning messages when sharing keys.

repository_tool.py methods that add keys to roles should also log a warning if it detects a shared key.
Add a console handler, and a function to disable it, to repository_tool.py.
Update _delete_obsolete_metatadata() docstring and comments in repository_tool.py.
Update tuf-spec.txt

Update section on supported cryptographic signatures.
Add some whitespace to improve readability.
Update repository_tool-diagram.png and comments.

Minor updates to comments of the previous repository_tool.py commit.
Update repository_tool-diagram.png to list disable_console_log_messages().
Rename disable_console_messages().
Merge pull request #170 from theupdateframework/repository-tools

Thanks given to Trishank, Santiago, Justin, Zane, Monzur, Lai, Dennis, and the appsec students for reviewing & testing the changes made in this pull request.
Remove find-code.sh

git-grep:
http://git-scm.com/docs/git-grep
http://travisjeffery.com/b/2012/02/search-a-git-repo-like-a-ninja/