API_HANDLER Module updated for only handling API

[sue-lim]

Implement API handler for external exchange service into Currency Script

[FEATURE] Currency Script | Implement API handler for external exchange service #431

Summary

Implemented api_handler module to handle the API Call.

Description

The changes are as follows:

• Updated api_handler for handling the api call and logic

Checks

in the repository

• Made no changes that degrades the functioning of the repository
• Gave each commit a better title (unlike updated README.md)

in the PR

• Followed the format of the pull_request_template
• Made the Pull Request in a small level (for the creator's wellfare)
• Tested the changes you made

Thank You,
Sue

[sue-lim]

@DhanushNehru - please kindly approve PR.