Extending support for Functions

[8hantanu]

To do:

Add tokenize and simplify support for different function classes.

Prereq:

Adding simplification support for the functions would be easier after simplify module is updated (#142)

Expected outcome:

• Create new Function classes or modify existing ones (trig, exp, log etc)
• Add support for tokenize and relevant checks for function input syntax
• Add simplification and plotting support (Crashes for some functions #118)
• Add integration and differentiation support for the new functions (Integration and derivative module  #32)

Edit:
Related issues: #118, #158, #160

[99bcsagar]

can i contribute