Number parsing - de-duplication of logic

[rudrajyotib]

Logic to parse number is duplicated in XML and JSON parser.
They can be moved to single place and be referred by both.

[rudrajyotib]

@stleary - I would like to incorporate the pending refactoring work around number conversion here. Please add hacktoberfest label.

[rudrajyotib]

@stleary - PR #814 814 raised.