Missing support for runlength encoded PC/PG composite types

[alibitek]

I see that this library is missing support for PC/PG composite types which require runlength decoding.

The wrdalib Python lib has this implemented already:

• http://wradlib.org/wradlib-docs/latest/generated/wradlib.io.read_RADOLAN_composite.html
• http://wradlib.org/wradlib-docs/0.9.0/notebooks/radolan/radolan_showcase.html#RADOLAN-PG/PC-Product

Test code: https://github.com/wradlib/wradlib/blob/master/wradlib/tests/test_io.py#L261

Call stack for PC/PG product type (top-bottom):

• read_RADOLAN_composite: https://github.com/wradlib/wradlib/blob/master/wradlib/io.py#L799
• https://github.com/wradlib/wradlib/blob/master/wradlib/io.py#L879
• decode_radolan_runlength_array: https://github.com/wradlib/wradlib/blob/master/wradlib/io.py#L689
• read_radolan_runlength_line: https://github.com/wradlib/wradlib/blob/master/wradlib/io.py#L663-L686
• decode_radolan_runlength_line: https://github.com/wradlib/wradlib/blob/master/wradlib/io.py#L605-L660

Would be nice to have support for runlength decoding formats in this C++ library also.

[kmuehlbauer]

@mnemonicflow Thanks for your suggestion. I'm not sure if PC/PG support will eventually implemented in libradolan. I won't have any time in the future, but @JuergenSimon might possibly find some time to think about it.

But anyway, if you want to take a stab at it, your PR is very welcome.