Implement base nucleus API

[Fishrock123]

From https://github.com/nucleus-js/design/blob/master/api/nucleus.md

Guide

Properties should be added in src/nucleus.rs.

The Duktape API is documented at http://duktape.org/api.html

Functions should be put in src/nucleus_functions.rs and accessed via nucleus_functions::your_fn. Functions should be exposed under this comment in src/nucleus.rs in the following manner:

duk::push_c_function(ctx, nucleus_functions::/* Your fn name */, /* number of arguments it accepts */);
duk::put_prop_string(ctx, -2, "/* your fn's JS name */");

If new duktape APIs are necessary they should probably be exposed in src/duk_api.rs for easy use and re-use.

A direct declaration of the duktape C api is required in the extern { } block.

The new exposed API should then drop the duk_ (it will be accessed via duk::) and handle the unsafe block and any major type conversions (such as CString).

New command line options can be added to this code in src/main.rs.

---

System

• [x] nucleus.cmd
• [ ] nucleus.args
• [x] nucleus.rawArgs
• [x] nucleus.exit(code)
• [ ] nucleus.getenv(name) -> value
• [ ] nucleus.setenv(name, value)
• [ ] nucleus.unsetenv(name)
• [x] nucleus.envkeys(showHidden) -> array of keys

  Runtime

• [x] nucleus.engine
• [ ] nucleus.compile(string, path) -> function

  Resources

• [ ] nucleus.base
• [x] nucleus.versions
• [x] nucleus.readfile(path) -> data
• [ ] nucleus.scandir(path, onEntry(name, type)) -> exists
• [x] nucleus.dofile(path) -> value
• [ ] nucleus.pathjoin(...parts) -> path

[Fishrock123]

nucleus.base and nucleus.compile should be quite easy now if someone wants to pick them up -- the relevant base_path handling code already exists in the code base, as well as a compile function for dofile.

[Fishrock123]

Hmm, looks like this guide is a bit out of date, will update soon. Most of the core bits should still be correct though.

Edit: done, I think.