i/c/mem.h: fix doxygen warnings, no functional changes
i/c/mem.h: fix doxygen warnings, no functional changes

Just fixing up the warning from doxygen so the documentation will be
more usable. Also fixing up some whitespace, punctiation marking and
indentation issues.

gebart/libcoap,gebart/libcoap,authmillenon/libcoap,authmillenon/libcoap,authmillenon/libcoap,gebart/libcoap