MSGIDs added to warnings and errors
MSGIDs added to warnings and errors

MSGIDs allow for better error checking.
Also used the built-in sprintf functionality of error/warning
where string concatenation was used.
Replaced errors starting with "Function XXX" with a proper
MSGID of the form  "matlab2tikz:XXX:msg"

okomarov/matlab2tikz,egeerardyn/matlab2tikz,matlab2tikz/matlab2tikz,PeterPablo/matlab2tikz,miscco/matlab2tikz,RPeschke/matlab2tikz,nidrosianDeath/matlab2tikz,okomarov/matlab2tikz,matlab2tikz/matlab2tikz,egeerardyn/matlab2tikz,LJeub/matlab2tikz