Common mappers implementation

[Siemienik]

The PR #20 refactor how the code is organised. Among others there was created new layer called mappers (src/mappers) and here I will describe how I plan to expand it.

Remark:

I marked this issue as good first issue because it contains list of simple and well described issues. Good practice is create one PR for one of these issues.

Actual

There is only file named index.ts with MAPPER_DEFAULT introduce in #19.

Expected

This should contains handy and the most popular mappers ready to use. The first mappers how I consider to do is:

• Add upperCaseMapper into mappers #23 upperCaseMaper: Some Text => SOME TEXT
• Add lowerCaseMapper into mappers #22 lowerCaseMaper : Some Text => some text
• Add isEmpty into mappers #37 isEmpty - true if has no value
• Add isFilled into mappers #39 isFilled - true if any value provided
• Add jsonMapper into mappers #40 jsonMapper : '{prop:[1,2]}' (string) => {prop:[1,2]} (object with array)
• Add splitMapper into mappers #24 splitMapper: val1,val2,val3 => [val1,val2,val3]
• Add numberMapper into mappers #46 numberMapper : 123 (string) => 123 (number)
• Add integerMapper into Mappers #48 integerMapper: Number.parseInt
• Add booleanMapper into mappers #53 booleanMapper: 0 => false
• Add dateMapper into mappers #58 dateMapper: transform date string into Date, same as new Date
• Add isValue into mappers #59 isValue - true if value match
• regexMapper - true if matches to regex EDIT: for further development
• decimalMapper: has to define **EDIT: ** for further development`

For each mapper I'm going to create new issue.

Request for a mapper

This issue is great a place to propose mappers, so if you have any idea, write a comment.

[Siemienik]

Reviewing #45 I note that, we haven't listed here some useful mappers:

• decimalMapper: has to define
• integerMapper: Number.parseInt
• dateMapper: transform date string into Date, same as new Date

I've just added it to the list above. I have to describe theirs test sets (data providers) and create issues.

[Siemienik]

As the PR #192 was done, This issue is fully accomplished 🥇 Thanks to all contributors for your efforts 🍰

Thank you:
@Metastasis @Gontrum @machadolucasvp