v0.6.0-beta

Three minor backwards-incompatible changes:

1. std.env is renamed to std.extVar. This is because environment variables are not the only way to get now-called 'external' variables into Jsonnet, you can also pass them explicitly on the command line (or via the library API).

2. The hidden status of fields defined with : is now preserved over inheritance instead of being reset by the base class. This means subobjects overriding fields from superobjects do not have to worry about whether those fields should appear in the output or not.

3. A new keyword tailcall is reserved for future use.

There are a number of enhancements to the standard library and interpreter, including the ability to generate multiple JSON files from a single authoritative Jsonnet configuration.