String Manipulation Functions for C02

Strings are zero-terminated arrays of type char with a maximum length
of 128 characters. 

The first character in a string is at position 0, and the last character 
is at position length - 1.

Since all of the routines stop processing at the 128th character, a 128
character string does not require a zero terminator.

Usage: at the beginning of the program use the directives

  #include <string.h02>
  
The following functions are defined:

  p = strchr(c, &s);  Searches string s for character c. 
                      
                      Returns position of character in string, or 255
                      if character was not found.
                      
  n = strlen(&s);     Determines length of string s.

                      Returns length of string.
                                         
  strset(&s);         Sets string s as the  source string for subsequent
                      strcat(). strcmp(), strcpy(), and strstr() calls.

                      Note: Sets variables srclo and srchi as a pointer
                      to the string.

  n = strcat(&s);     Concatenates destination string s onto the end of
                      source string set by prior setstr() call.
                       
                      Returns total length of concatenated string.

                      Note: srclo and srchi are left pointing to the
                      source string.
                  
  b = strcmp(&s);     Compares destination string s against source 
                      string set by prior setstr() call.
                       
                      Returns -1 if source < destination, 0 if 
                      source = destination, and 1 if source > destination.
                  
                      Note: srclo and srchi are left pointing to the
                      source string.
                                    
  n = strcpy(&s);     Copies destination string s into source string 
                      set by prior setstr() call, replacing previous
                      contents.
                      
                      Returns number of characters copied.
                      
                      Note: srclo and srchi are left pointing to the
                      source string.

  p = strstr(&s);     Searches for destination string s in source string 
                      set by prior setstr() call.
                      
                      Returns position of destination string in source
                      string, or 255 if character was not found.
                      
                      Note: srclo and srchi are left pointing to the
                      address of the position of the destination string 
                      in the source string.

Note: This library expects the following Zero Page locations to be defined
  
  strlo, strhi        Destination String Pointer 
  srclo, srchi        String Pointer (high byte)

as well as the memory location 

  temp0               Temporary storage