Remove typename prefix from feature ids when importing from GeoTools DataStores

Documentation has been modified to reflect the above changes
Improved usage of exit codes in CLI commands

Some CLI commands print error/warning messages to the console in case of failure, and exit with a zero exit code. This commit fixes that, so all CLI commands exit with non-zero exit code whenever the operation was not succesfully performed.

The commit includes some light cleaning in api operations
Merge pull request #295 from volaya/replace_fid

Remove typename prefix from feature ids when importing from GeoTools DataStores
Merge pull request #256 from volaya/exit_code

Improved usage of exit codes in CLI commands