simplify(): Call piecewise_fold for expr with Piecewise (issue 3902)
Fix tests after adding piecewise_fold to simplify()
Don't renumber constant symbols inside of Piecewise
Merge pull request #2205 from skirpichev/3902-piecewise_fold

simplify(): Call piecewise_fold for expr with Piecewise (issue 3902)
remove is_finite from Add.flatten
remove is_finite from limits
remove is_finite from core/numbers.py
Merge pull request #2211 from mrocklin/remove_is_finite

Remove is_finite
Added WIP frame file
Added functions map_variables, removed __new__
Coded initialiser and time_derivative methods
Added auxiliary functions file, added convert_pos_vector function
Added new initialiser, changed tree implementation
Changed tree implementation to avoid tranversing entire tree
Added support for tuple args, recitified trans methods