All instances of projectrekor are now renamed to SigStore

This includes:

* Import paths
* Tests
* Readme's

Signed-off-by: Luke Hinds <lhinds@redhat.com>

fixes #149

Signed-off-by: Luke Hinds <lhinds@redhat.com>

* README updates

Details on how to build the server and verify amendments

Implement upload command

Accept flags artifact-url,public-key, signature and validate GPG formatting and verify file signature

* Remove unsed files (log_server, inclusion (which is now get)

* Add some meaningful text to CLI help

* Make the README more specific to the new role of the CLI (direct
connections to rekor server)

map server not needed