Fix in TFormula the parsing of user defined functions which contain pre-defined functions (e.g. gaus) in their name. Fixes ROOT-10815.
For example when a user defines a function with the name "f1gaus" and then reuses that name could cause in same case an error parsing the expression.
Example :
```
TF1 f1("f1gaus","gaus");
TF1 f2("f2gaus","f1gaus+gaus(3)");
```
If the function name is for example  "fgaus" it was working before, but not if a character number is used before the pre-defined function name such as  "f1gaus".

Add also a test for parsing these cases in TFormulaParsingTest.

This commit fixes ROOT-10815

Also add test cases for invalid formulae. And fix |= to &= - better all
tests be successful instead of any one.

Fix ROOT-9801, by correctly copying the members for lazy initialization in TFormula::Copy. Add also a test for reproducing ROOT-9801

Add a test of TFormulal::Print

Fix correctly hanflying of whitespace in parameter names. Due to a bug in handling the parameter name, reconstruction a function from an expression with white space did not work

* 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

Fix ROOT-8303. Handle special characters (such as ^,@ or predefined-functions characters) in parameter names.

Fix Formula for missing parameters, ROOT-8182, e.g. TFormula(“f”,“[0]+[2]”) has now 3 parameters and not 2. The second parameter, “p1” is a ghost one.
This restores backward compatibility with old TFormula.
Add also a test

Add corresponding test

Add new tests showing cases which were failing before (test34,35,36)

Add also a corresponding test

Added compilation flag  -Wshadow for cling and gcc. Fixes ROOT-7378 Insufficient warning level with CMake

Fix handling of composite polynomial functions. They are not linear and the number should be zero. This fixes also ROOT-7755

Handle also better cases when function name was contained in other name (e.g. sq and sqrt)

Change TMath::Sign for inter types to be a templated T1 Math::Sign(T1, T2). This fixes problem of Sign(1,double(x)) observed in TFormula.
ROOT-7375.
Add also an overload of TMath::Sign for LongDouble

This required some changes in the handling of function shortcuts and the loop in ProcessFormula needed to be split in two.
Add also function "sign" and tests for "sq" and "sign" functions.