Add support for `URLENCODE` function

[mitya57]

Change Summary

This adds URLENCODE that percent-encodes special characters, so that column value can be safely substituted into URLs.

Change type

• [x] feat: (new feature for the user, not a new feature for build script)
• [ ] fix: (bug fix for the user, not a fix to a build script)
• [ ] docs: (changes to the documentation)
• [ ] style: (formatting, missing semi colons, etc; no production code change)
• [ ] refactor: (refactoring production code, eg. renaming a variable)
• [ ] test: (adding missing tests, refactoring tests; no production code change)
• [ ] chore: (updating grunt tasks etc; no production code change)

Test/ Verification

Tested on PostgreSQL. But it should work fine on other backends, too.

[CLAassistant]

All committers have signed the CLA.

[mitya57]

You may probably just use REPLACE or REGEX_REPLACE in knex.raw to encode those special characters specified in RFC 3986.

Okay, I implemented that approach. I used the list of characters in RFC 3986 section 2.2, but I removed characters that encodeURIComponent() does not encode, and added percent sign and space.

Please review again.

[mitya57]

Here is how it looks now:

[mitya57]

Rebased on top of the latest develop branch to fix the conflicts. @wingkwong, @pranavxc Please review again.

[mitya57]

Fixed a stupid copy-paste error in tests, now they should pass.

[mitya57]

Improved the documentation.

[mitya57]

Ping please? Just rebased again.

[wingkwong]

Re-running the tests.