Grass-gis-helpers

Added
- add function `test_installed_addon()` for testing if a specified addon is already installed 28

Added
* add function `test_memory()` for testing if desired memory is available 25

Changed
* rename function `free_ram()` to `get_free_ram()` for fitting python function naming 25
* `How-to-create-a-GRASS-GIS-addon.md`: markdown formatting 24
* Enhance `How-to-create-a-GRASS-GIS-addon` README 23

Added
* added function for extracting files using zipfile_deflate64 [22](https://github.com/mundialis/grass-gis-helpers/pull/22)

Fixed
* Add requests to dependencies

Added
* Add import_administrative_boundaries 21

Added
- Open geodata germany and other data import functions 18
- Add vector import functions 19

Fixed
- Fix typos 20