Inline context initialization & improve _object.value

* Context setup is now done via _newContext.
* _newContext is a function that resides in inline.go. _newContext is very flat,
resulting in almost no function calls (a 180 from the earlier status quo).
* inline.go is a Go source file that is built by Perl (via inline).
* Lots of crufty functions removed (along with all of their TODO & FIXME).
* In addition, before, the underlying value of _object.value was a pointer to
something. This made for extra work, since the type of _object.value is interface{},
which is already something of a pointer. Now, the underlying value of _object.value
in Function, Date, RegExp, ..., is a struct value.
* type_function.go was streamlined, removing superfluous struct fields and methods.
* There is now less "digging" to get to the actual value of a function, which is important
when makings lots of calls.

Before (without inline):

    PASS
    BenchmarkNew        2000           1067871 ns/op
    ok      github.com/robertkrimen/otto    3.336s
    PASS
    BenchmarkNew        2000           1077644 ns/op
    ok      github.com/robertkrimen/otto    3.367s

After (with inline):

    PASS
    BenchmarkNew       10000            364418 ns/op
    ok      github.com/robertkrimen/otto    4.616s
    PASS
    BenchmarkNew       10000            307241 ns/op
    ok      github.com/robertkrimen/otto    4.051s

This (partially) fixes #22
Fix documentation

This fixes #26
Embiggen test for #24

Make sure we get back out what we put in.