Eptr2

+ There are now aliases that can point to calls. For instance, "ptf" also points to "mcp" call. More aliases to come in the future.
+ `custom_aliases` parameter is introduced (see Readme for detailed explanation) so that you can define your own aliases.
+ Some NG-VGP calls had either period and start-end date parameter set distinctions. Wrapper functions are built for the calls.

+ New natural gas calls. Natural gas calls are completely covered.
+ Totaling up to 175 calls.
+ Some minor fixes and improvements.

+ Added 15 more natural gas calls. Some more to go.
+ Some simplifications for the path mapping (background improvements, insignificant at runs)

This version adds new natural gas calls. You can see the list of calls beginning with "ng-" prefix with the command `EPTR2().get_available_calls()`.

Updating to this version is recommended if you have long running (>8 hrs) transparency processes.

- Minor bug to prevent automatic TGT check is fixed
- A deprecation warning is converted to yield error
- 5 new calls for retrospective adjustment (GDDK) are added

datetime package of some Python versions had a problem with `fromisoformat` method when parsing TGT start time. With this fix start time defaults to `now` if any error occurs.