Added Windows support

[snake-4]

• Added support for Windows platform with instructions in the README file.
• Made some changes to the starch's python code and templates which were required for the Windows support. I can make a PR - on the starch's repo instead as well for this.
• Fixed a typo and added the default values in the help text of HackRF's arguments, there are no other changes to any SDR interface code.
• Added a file for the math constants to minimize the dependency on non-standard C extensions. While there are still non-standard extensions used such as the nanosleep, strdup, they can be changed in the future.

For Windows builds, the required DLL files have to be copied manually to the build folder.
The DLL files required by a dump1090 build with all SDR integration code enabled and compiled with MinGW-w64 10.3 are as follows:
bladeRF.dll hackrf.dll libiconv-2.dll libintl-8.dll libsystre-0.dll libtre-5.dll libwinpthread-1.dll LimeSuite.dll rtlsdr.dll
These files can change depending on the compiler used.

I've tried to modify the CI files for the changed src path but I'm not sure if they work.
Compiles fine on both Ubuntu(GCC 9.3.0) and Windows(MSYS2 MinGW-w64 10.3) without any warnings.

Note: Dependent on #140, the dependency has to be merged first!
Note: Only the last commit in this PR is relevant, the other commits are all from the PR #140 which does not modify any source files.

[mutability]

I can probably take these individually, if you're willing to break them out into separate PRs

• starch changes (please PR against the starch repo)
• hacksdr fixes
• the math portability stuff

The overall Windows support I probably can't take until at least after the 6.0 release which is coming up soon - it's too close to add something big like that unfortunately.

The dependency on #140 unfortunately means I can't do much with this PR until #140 is resolved one way or another

[snake-4]

Created a PR on the starch repo. Will undo the changes here once that gets merged into the dev branch of this repo.