* add NSUM functionality to TF1

* parse NSUM in TF1

* uncommented cout-s

* adding parameter specification to TFormula (WIP)

* basic parsing of user-defined functions (need to make more robust)

* fix parameter naming; partially fix ReplaceAllName

* mostly fix ReplaceAllName; HandleUserFunctions works on easy cases

* fix parameter naming

* fix ReplaceAllName (again\!) ; add parameter-only option (not well tested)

* easy parametrized function case working (still not robust)

* replacements take place in parallel now

* swaps working properly

* add argument parsing for parametrized functions

* add parsing test for user-functions with arguments

* add parameter range shortcut (e.g. [1..3])

* can parse variables given in form "x[N]"

* inherit parameter values (iff parameter names match)

* fix bug about undefined parameters when using NSUM

* fix whitespace; add a few comments

* run clang-format

* add test for nested functions

* apply clang-format

* fix memory leaks

* clang format (again\!)

* clang-format (missed two lines last time!)

* add documentation to TFormula