Rename builtin and core module functions

[ThakeeNathees]

BREAKING CHANGE -- Till the first release, it's most likely to change everything with compatibility breaks.

Discuession

Currently, pocketlang doesn't have any naming convention, and every symbol is snake_case. We need to enforce a naming convention for consistency across the builtin functions and core modules. And I'd like it to match our C implementation.

• Function names are camelCase

• Variable names/attributes are snake_case

• Class names are PascalCase

• Modules intended to used as a collection of functions (ex math, path) - snake_case

• Modules intended to used as a type wrapper (ex File, Fiber) - PascalCalse

How to rename

• You can find all the builtin functions, core module and its functions at src/pk_core.c Here (ex: to_string -> toString)

• The additional cli modules at cli/modules.c

Finally

• This requires you to rename all the test suites in tests/ directory for the tests to be passed
• Check docs at docs/pages/Getting-Started/learn-in-15-minutes.md if any functions need renaming.

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If you have any suggestions, regarding the renaming let me know.