lib, test: general improvements related to find-python.js

- test/test-find-python-script.js
  rephrase comment

- test/test-find-python.js
  fix equality expression in testExecFile func, which led
  to wrong function behavior

- lib/find-python.js
  - organize colors for highlighting output in single object
  - change the way errors are passed:
    now there is new class ErrorWithData to
    fit the propose to pass additional data along the error.
    Now any error capable object can be thrown

  - general improvements to comments:
    add additional explanations,
    expand documentation,
    provide thoughts about checkPyLauncher,
    outline potential bug with powershell and quoted string on windows,

  - fix error message in "checkExecPath",
  - add version in "checkExecPath" to silly log and return silly logs
    from previous version of "run" function

  -

Author: owl-from-hogvarts