ecc: add some more documentation
ecc: add some more documentation

Signed-off-by: Hauke Mehrtens <435ddd46dc66c007a1fa20144c823d37e0d23436@hauke-m.de>

OlegHahm/tinydtls,fvdnabee/tinydtls,nmacs/tinydtls,nmacs/tinydtls,jvermillard/tinydtls,jvermillard/tinydtls,thecodemaiden/tinydtls-fork,yunus/TinyDTLS-WebID,yunus/TinyDTLS-WebID,thecodemaiden/tinydtls-fork,spark/tinydtls,nmacs/tinydtls,spark/tinydtls,OlegHahm/tinydtls,nmacs/tinydtls,yunus/TinyDTLS-WebID,OlegHahm/tinydtls,fvdnabee/tinydtls,fvdnabee/tinydtls,jvermillard/tinydtls,spark/tinydtls,thecodemaiden/tinydtls-fork