Added path expansion to blocks.

This includes modification of command.py to take a file_root as an
argument, and locations.py to identify not only absolute paths, as in
os.path.isabs, but also those prefixed with variables.
Changed access to block attrs to use get() and set() accessor and mutator.
Switched to use BlockExceptions instead of asserts in block.py

Also added better comments to block.py
Merge branch 'feature/relative-path-expansion' into dev
Upgraded README to v0.0.2
Merge branch 'documentation/readme-0.0.2' into dev
Added test utils package.

tests/utils handles the common desire to ensure an exception is raised.
This includes a stubby version of the commandline testsuite.
Expanded the commandline testsuite.

Includes specification of a future test for git repos which currently
raises a SkipTest and some commandline parsing checks.
Merge branch 'feature/tests/commandline' into dev
Separated blocks into their own package.

Although blocks were originally a component of the execution package,
they play an important role both in the parser and as an intermediate
representation in their own right. This separates them into their own
package in src/block and does the same for block tests.
Made file expands require a specified root_dir

This made it necessary to add this constraint to block expansion as
well. Includes updates to the unit tests to accept this behavior.
Fixed path expansion with vars in relative paths.

There was a standing bug in which a relative path that contained a
variable was expanded before variable substitution. The code is now
cleaner so that this is no longer a possibility.
Merge branch 'feature/refactor/block-package' into dev
Slight expansion of SALVE Langue spec in README
Merge branch 'documentation/readme-language' into dev
Merge branch 'dev' into nightly