Add `getPublicKeyFromInput()` to `Transaction` class

[theanmolsharma]

Add the following function to Transaction class

getPublicKeyFromInput(index: number): Buffer | null {}

This function should extract the public key from the script or witness property of the input whichever is relevant based on the input type. The following output script types contain public key in script:

• P2PKH

The following output script types contain public key in witness:

• P2WPKH
• P2SH-P2WPKH

For all other script types, the function should return null

[rajarshimaitra]

Same as the other one. How about Options?

And also a doc of this behavior on the functions, explaining which one throws None and why.

[theanmolsharma]

Same as the other one. How about Options?

And also a doc of this behavior on the functions, explaining which one throws None and why.

replied in #12