Added public domain implementations of strchr and strstr.
logo gradients in master SVG, png

Also new vector_log png with alpha
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.
Add MP_OBJ_TYPE(o) accessor.

Should not be overused, but when needed, it's needed.
rt_is_true(): Start with testing for (expected) boolean values.
Add rt_resolve_method() which doesn't throw exception if method not found.

Unlike previosuly existing rt_load_method().
Add objtuple.h to allow embedding of tuples inside other objects.

This is useful because tuple is closest analog of C static array.
Refactor exception objects to have better impl of Python-side interface.

This implements internal args tuple of arguments, while still keeping
object useful for reporting C-side errors.

Further elaboration is needed.
type->print(): Distinguish str() and repr() variety by passing extra param.
Implement str() and repr() builtin functions.
Move mp_obj_int_t definition to objint.h, to reuse in long int impls.