* Implemented Native function as IExprs so we can refer to them
like any other function. Checkout `NativeFunction`.
* `require` has been implemented as a native functions which
accepts one or more namespace descriptions and load them.
A namespace description is either a symbol with the ns name
or an `IColl` in the following form `(some.ns.name alias).
* A hashmap of strings to native functions has been added to the Runtime
which is used to resolve builtin functions.
Added the support for normal macro (in compare to reader macros and
other types) expansion with out quasiquote support. The quasiquote
will be added as a recursive macro itself.
Sameer Rahmani