Update bitcoinunits.cpp

Adding a name for the smallest possible unit. :>
Update bitcoinunits.cpp
Update bitcoinunits.h

Adding Koinu @leofidus :D
add megadoge and kilodoge as selectable units
remove millidoge and microdoge units

Users who have set them as display unit fall back to Doge with this change
Merge branch 'master' of github.com:inutoshi/inutoshi