Units longnames

A previous branch lengthens all the CODE names of the non-SI units. This one lengthens all enumeration strings to decrease the chances of collisions both with other enumerations and with macros in C++. For example:

 * `MM` --> `MILLIMETER`
 * `LY` --> `LIGHTYEAR`
 * `S` --> `SECOND`
 * etc. 

The passing of the jobs should suffice for testing, though suggestions for different namings are also welcome. (Beware of typos) Some open PRs may be using enumerations which are changed here.