improved na handling fornum parametre
added better validation for xSortBy
updated readme docs
changing branch
updated summation
added worksWhen, which tests if an expression runs at all.
added test for take and drop
updated docs
added test to tabulate
added missing export
added new reverse test
added restof test
added more tests.
added flatmap test
fixed dangerously failing test.
added several tests
refactored forall to run in order of increasing length
fixed syntax error
improved generators
updated function composition.