multiprocessing for sencha translate

[pranathivemuri]

will work on top of #88

PR #88 has added changes where the pandas dataframe was creating with the coding scores, now we just use a list of scores instead This PR adds multiprocessing and does a map-reduce-combine approach -

• map - by splitting the fasta file into several chunks and
• reduce - then processing each of them on a core and all the results instead of being returned they are written to intermediate files (this is to avoid usage of RAM and pickling errors where the attributes are too large to pickle - https://stackoverflow.com/questions/47776486/python-struct-error-i-format-requires-2147483648-number-2147483647), also declares nodegraph as global variable as it is not picklable.
• combine - Combining is done on the results written by each of the processes

For this to work two flags are introduced intermediate_directory and processes

PR checklist

• [x] This comment contains a description of changes (with reason)
• [ ] If you've fixed a bug or added code that should be tested, add tests!
• [x] Ensure the test suite passes with pytest . (command to run: pytest or make coverage if you want to see which lines don't have tests yet)
• [x] Make sure your code is linted and autoformatted using black (black . --check).
• [ ] Documentation in usage.md is updated
• [ ] README.md is updated