Added public domain implementations of strchr and strstr.
Initialize is_kw for dynamically allocated mp_obj_fun_native_t ojects.

This should fix issue #171
Merge pull request #172 from dhylands/init-kw

Initialize is_kw for dynamically allocated mp_obj_fun_native_t ojects.
Cleanup built-ins, and fix some compiler warnings/errors.
Merge pull request #168 from dhylands/add-strstr

Added public domain implementations of strchr and strstr.
Consolidate rt_make_function_[0123] to rt_make_function_n.
Move mp_obj_int_t definition to objint.h, to reuse in long int impls.
mp_obj_equal(): Compare small and long ints properly.

By dispatching to long int methods.
Merge remote-tracking branch 'upstream/master'