Added readme.
Added function to get the first commit date.

The function implementation for get_first_commit_date is still a placeholder.
Implement set_project_id.

The function set_project_id will now actually set the project code on a Fossil repository. No error checking of input parameters is performed however.
s/project_id/project_code/g

Fossil refers to the value as the project code, so project_id was renamed to be consistent.
Implemented get_project_code.

The project code of a Fossil repository is now retrieved by get_project_code. The repository shadow now has the same project code as the reference repository.