Optimize for both speed and size

[eliasbakken]

As suggested by Kevin O'Connor, it can be a good idea to optimize most of the code base for size, but some of it for speed.
For instance __attribute__((optimize("O2"))) on stepper related commands.

[goeland86]

This is just an off-the-cuff thought, but on Gentoo, gcc optimizations for 02 are for speed, but 03 are speed and compressed instructions. I'm not all that familiar with the 0s Kevin referred to in the PR comment, but from what I recall, the 03 is meant to keep the speed optimizations while also compressing the code - it may not be as compressed as a pure size compression algorithm though.

[goeland86]

Ok, this page on what the different gcc parameters do should help:
https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html
I remembered it wrong, the -03 is just even faster optimizations, while -0s is the -02 without size increases.