Add Support for JSONL Writer

[mzaeemz]

This PR has the objective of adding support for writing to JSONL files

Changes

1. Updated tojson function in petl.io.json to write in JSONL format if lines argument is set to true

Checklist

Use this checklist for assuring the quality of pull requests that include new code and or make changes to existing code.

• [x] Source Code rules apply:
  • [x] Includes unit tests
  • [x] New functions have docstrings with examples that can be run with doctest
  • [x] New functions are included in API docs
  • [x] Docstrings include notes for any changes to API or behaviour
  • [x] All changes are documented in docs/changes.rst
• [ ] Versioning and history tracking rules apply:
  • [x] Using atomic commits when possible
  • [x] Commits are reversible when possible
  • [x] There is no incomplete changes in the pull request
  • [x] There is no accidental garbage added in source code
• [x] Testing rules apply:
  • [x] Tested locally using tox / pytest
  • [x] Automated testing passes (see CI)
  • [x] Unit test coverage has not decreased (see Coveralls)
• [ ] State of these changes is:
  • [ ] Just a proof of concept
  • [ ] Work in progress / Further changes needed
  • [x] Ready to review
  • [ ] Ready to merge

[coveralls]

Pull Request Test Coverage Report for Build 3111981167

• 42 of 43 (97.67%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 91.117%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
petl/io/json.py	10	11	90.91%
<!--	Total:	42	43	97.67%	-->

Totals
Change from base Build 2899567235:	0.02%
Covered Lines:	12750
Relevant Lines:	13993

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💛 - Coveralls

[mzaeemz]

@juarezr Thank you for the feedback. However, my noob self ended up deleting the branch. I have created a new PR here, kindly take a look at it.