Add Changelog for v0.4.0

[dmlb2000]

jsonpath2 version

v0.3.1

Platform Details

Any

Scenario:

Want to get the latest version of the code.

Steps to Reproduce:

pip install jsonpath2

Expected Result:

Stuff that's in master of the git repo...

Actual Result:

Couple of revisions past and that's got some good stuff in it!

[dmlb2000]

Fixed in #29