Define & warn against using jQuery.parseJSON

[mgol]

In jQuery 3.0.0 jQuery.parseJSON will be deprecated (PR: jquery/jquery#2948). Migrate should redefine it (a one-liner) and warn about using it.

[mgol]

Since I made this issue necessary (this was initially planned for jQuery 3.1.0) I'll take this one. :-)

[mgol]

PR: #153