For example, don't pass Integer to double method. This is still not
selective enough to choose the right overloaded method maong those
taking objects.

Incluides several improvements and a few API changes to comply
with the new hardware API.

The UART REPL it's not enabled by default anymore.

If VT100 support is not available then a given implementation of
mp_hal_erase_line_from_cursor might need to know the number of characters
to erase.

This patch does not change generated code when VT100 is supported, since
compiler can optimise away the argument.

This saves around 1000 bytes (Thumb2 arch) because in repr "C" it is
costly to check and extract a qstr.  So making such check/extract a
function instead of a macro saves lots of code space.

This new object representation puts floats into the object word instead
of on the heap, at the expense of reducing their precision to 30 bits.
It only makes sense when the word size is 32-bits.

Simple smoke tests, mostly for coverage. Added to extmod based on the fact
that they're extensions to standard modules.