Refactor find.turn.point.R and find.tol.time.R and recover.weaker.R

[wverastegui]

Refactored find.tol.time.R and find.turn.point.R. The pastecs library has been added to use the Turnpoint function in find.turn.point.R, that simplifies the code. Added pastecs to dependencies.

Closes #90
Closes #77

This PR now also includes the changes from #92 to fix the overarching test cases, as fixing the things for this PR would require changes in other functions, so I decided to append all changes from #92 here.

• Extracted all functions performing substeps of the computation
• Renamed variables to better reflect the data they actually contain
• Disabled parallelism in test case for better debugging
• Working toward isolating executions on individual files to ease implementing a parallel version in Galaxy
• Added documentation to all extracted functions
• Added stubs for further simplifications which might be more drastical code changes --> those need to be validated in extended tests

Closes #74

[wverastegui]

find.turn.pint.R was reverted to refactored version, Turnpoint function prevents passing the tests. Changelog file was updated accordingly (96c64ae)

[xtrojak]

Consider spending more time with the merge, I think the final version could benefit from both your and my refactored versions.

[hechth]

Consider spending more time with the merge, I think the final version could benefit from both your and my refactored versions.

Thanks for the hint - I'll have a better look and see how to merge it better! Thanks for paying attention to details :)