reimplement row min in C ref #20

[schochastics]

looking good except

File ‘quanteda.proximity/libs/quanteda.proximity.so’:
    Found no calls to: ‘R_registerRoutines’, ‘R_useDynamicSymbols’
  
  It is good practice to register native routines and to disable symbol
  search.
  
  See ‘Writing portable packages’ in the ‘Writing R Extensions’ manual.

https://stackoverflow.com/questions/42313373/r-cmd-check-note-found-no-calls-to-r-registerroutines-r-usedynamicsymbols

[schochastics]

I think it is done