Remove erroneous reference to `path` in description and error list;
add format description for `id` string;
add "invalid format" error for `id` string;
remove initial capitals on references to parameter names;
remove reference to `initialConfig`;
add description of id checking.

Signed-off-by: Steve Powell <spowell@pivotal.io>
Merge pull request #172 from cf-guardian/create-api

Correct Create() api call description in Factory interface.