Type hints and static type checking for PyElastica

[bhosale2]

We should have type hints and static type checking throughout PyElastica using mypy, which adds more context to function arguments and reduces the chances of error while coding.

[ankith26]

Hello! I'd like to work on this issue if @armantekinalp hasn't started work on this already, and wants me to instead.

[armantekinalp]

sure go ahead