add unit_tests

[aerorahul]

This PR adds unit tests from @jbathegit .

• It includes a bugfix, where c_hdr were not available under build interface.
• Adds ctests for tests from @jbathegit
• README is translated into Markdown format.
• The test data is downloaded from https://ftp.emc.ncep.noaa.gov/public/bufr.tar.
• added github action to run tests on push and PR.

Testing:

• All _4 and _d tests pass. _8 tests don't. I think that is expected.
• OUT3 tests do not compile on GNU and hence cannot be tested. Compiles and runs on Intel.

Help wanted!
I cannot figure out why test_OUT_3.f won't compile with GNU and dynamic allocation.
On Intel, the test compiles.

On Intel and GNU, _8 tests exhibit failures. This will need careful look at the test codes itself.

[mark-a-potts]

All the tests other than the _8 ones pass for me using both GNU and Intel on Hera.

[aerorahul]

I think @jbathegit did not intend to run test the _8 library, but I may be wrong.
we can wait for @jbathegit to return and give us instructions oh how he wishes to proceed.

[aerorahul]

Changing this to an actual PR.

[mark-a-potts]

This looks good to me. Worked with no problems on my generic linux box using GNU. My only question is whether we should have the ENABLE_TESTING default to ON instead of OFF.

[aerorahul]

This looks good to me. Worked with no problems on my generic linux box using GNU. My only question is whether we should have the ENABLE_TESTING default to ON instead of OFF.

I was just keeping the defaults as other NCEPLIBS. @kgerheiser has the defaults to ENABLE_TESTS=OFF. A push and PR triggers tests on github.
I am happy to turn it ON, @kgerheiser?

[jbathegit]

Looks OK to me, and thanks for integrating these into the build environment!