Add support for dotenv file

Example of .env file:

#
# SPICE kernels location
#
KERNELS_JUICE=/data/ESA/JUICE/kernels
KERNELS_EUROPA_CLIPPER=../kernels/Clipper

Added

• TourConfig now supports .env file to locate the mission kernels directories. This will simplify the way people can defined the location of there kernels without having to hardcode their paths. It also allow the user to locally bypass their global configuration if needed.

• New dotenv file finder function to locate .env files in the current working directory or any of its parents:

from moon_coverage.misc import find_dotenv

find_dotenv()

Path('/path/to/.env')

Note: only the first .env is returned.

• If a .env file is found, its environment variables will be loaded instead of the global env variables. You can check which env variable is loaded with the getenv function:

from moon_coverage.misc import getenv

getenv('KERNELS_JUICE')

'/data/ESA/JUICE/kernels'

Note: Dotenv variables don't modify the global variables (os.environ).

• To have a list of all the kernels directories available, you can now use the print_kernels_dir() function:

from moon_coverage import print_kernels_dir

print_kernels_dir()

Dotenv file found:
- .env

Kernels ENV variables:
- KERNELS_JUICE         : /data/ESA/JUICE/kernels (.env)
- KERNELS_EUROPA_CLIPPER: ../kernels/Clipper (.env)

• You can also use %load_ext moon_coverage magic function for IPython/Jupyter environment to directly the tool configuration:

%load_ext moon_coverage

Installed packages:
- moon-coverage: 0.12.0
- esa-ptr      : 1.0
- numpy        : 1.23.5
- matplotlib   : 3.6.2
- spiceypy     : 5.1.2

Dotenv file found:
- .env

Kernels ENV variables:
- KERNELS_JUICE         : ../kernels/JUICE (.env)
- KERNELS_EUROPA_CLIPPER: /data/kernels/Clipper

• We also simplify the documentation on TourConfig to reflect these changes and encourage the user to use global env variable or .env files.

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Closes #65 (closed).