Build path should reflect Python version

[mlouielu]

Spacetime BUILD_PATH is hard-coded as dev37 or dbg37.

It should somehow reflect the Python version used in the compile time:

$ make
...
-- Found PythonInterp: /usr/bin/python3.8 (found version "3.8.3") 
-- Found PythonLibs: /usr/lib/libpython3.8.so
-- pybind11_INCLUDE_DIRS: /usr/include;/usr/include/python3.8
...
-- Generating done
-- Build files have been written to: /dev/turgon/spacetime/build/dev37
make -C build/dev37 VERBOSE= _libst
make[1]: Entering directory '/dev/turgon/spacetime/build/dev37'
...

[mlouielu]

Trick like this will work:

➜  spacetime git:(master) ✗ python -c 'import sys; print(str(sys.version_info.major) + str(sys.version_info.minor))'
38

But Guido said there will have Python 3.10 1, then this trick output 310, hmm

[yungyuc]

I think it makes sense. Do you mind to make a PR?

[mlouielu]

No problem.