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
Rectified mistakes in code
Added docs, finalised functions and removed unnecessary reexpressions
PEP8 modifications and rectified typos
Added Particle class
Rectifications as per review
Added dynamicsymbols to core, rectifications as per ad-hoc tests
Added tests for functions.py
Added support for tuple-type rotation boundary conditions
Added some tests for frame.py
Added more tests