Build succeeds even if SWIG is not found, breaking examples.

[pgorczak]

Building without SWIG seems to work fine but it breaks the examples, resulting e.g. in #11.

Is SWIG always required for gr-lora to work? If it is, we should make the build fail if it can't be found, by changing CMakeLists.txt line 31 to

find_package(SWIG REQUIRED)

If there are cases where you want to just skip the Python bindings, we could instead add a warning before CMakeLists.txt line 34 like

message(WARNING "SWIG or Python-libs not found. Skipping Python bindings.")
message(WARNING "Note that examples won't work!")

Since I'm a total GNUradio noob, I can't tell which one is right, so not opening a PR yet ¯\_(ツ)_/¯

[matt-knight]

Hi @pgorczak,

Thanks for noting this. While technically one can use GNU Radio without the Python layer (thus not requiring SWIG), I don't know a single person who does this. So I am of the opinion that your first solution mandating the use of SWIG is the way to go.

I'm happy to handle this, unless you'd rather do the honors.

Best,
Matt

[pgorczak]

Hey I just opened #21 after seeing how easy minor edits are from the website :)