translator: changed handling of current token

instead of passing the current token (which is possibly unset) into and
out of each of the functions, the current token is now kept in a member
variable, where functions leave it set to the token that terminates them
or consume it (leave it empty) if successfully processing the token;
the token reference argument was therefore removed from these functions

added check to get token to only get token if member token not set
moved process command code into get commands
removed command token and token arguments from command translates
added get, reset and move current token access functions
added reference argument to process internal function
(instead of setting token reference flag for sub-string assignments)
moved setting of define function code to process parentheses token
changed rpn list token access function to return a reference
reorganized some of the code
renamed local token variables to just 'token'
updated comments for changes