Teach mirb another way to quit

Add CMake support authorship miss

call mrb_close() in tools and test programs

Avoid warning: redundant redeclaration of ‘OnigEncDefaultCharEncoding’

Add CMake build infrastructure

I was hoping this would cause valgrind to complain less, but there is still
a lot of memory leaked (does mrb_close() actually free all of the managed
blocks?)  Anyway this helps somewhat and is good practice

Conflicts:
	src/time.c

As per monaka's comment here...
  https://github.com/mruby/mruby/pull/175
...changing these initializations of mrb_int values to use integer
constants

* mrb_time_gm() uses mrb_int
* Same for mrb_time_initialize()
* The parameters to time_mktime() are mrb_int, and that's what these values are passed to

So I don't see why mrb_time_local() works on mrb_float instead.  Lets make
it consistent with the other methods defined in time.c

More C++ compilability work: mrb_obj_alloc void* conversions

One of the biggest set of changes needed to make C++ compile, is that you
can't autoconvert "void*" to a different pointer type without a cast (you
can of course, convert pointers *to* "void*"!)

For the first part, convert the users of "mrb_obj_alloc".  Since it has
to return something, make it RBasic* (that's what mrb_obj_alloc() is
operating on anyway).  This way, even in C you'll get a warning if you
don't cast it.

For places where there are a lot of similar calls to mrb_obj_alloc(),
this can be easily hidden through a macro.  I did this in string.c:
    #define mrb_obj_alloc_string(mrb) ((struct RString *) mrb_obj_alloc((mrb), MRB_TT_STRING, (mrb)->string_class))

I also updated the mrb_object() macro to also return a RBasic* -- my
previous commit changed that from "void*" -> "RObject*", but I figure
it should be consistent with mrb_obj_alloc()