[README.md] some changes and additions

Changed web addresses from mbed.org to developer.mbed.org, added some
Nucleo and one Discovery board, reorder of the Nucleo boards depending
on M0, M3, M4.
[README.md] some more changes and additions

Some more web addresses changes and added CoIDE as toolchain.
Merge pull request #545 from ohagendorf/master

README.md - some changes and additions