Evaluate and implement a fix for echod serial characters

[PropGit]

Regarding echoed characters as indicated by BlocklyProp's Issue #690, (Look for posts describing "An underlying function inside of getStr() is generating an echo"), we need to evaluate and fix this in Simple Libraries.

[MatzElectronics]

I have some candidate code for this, but since I'm here, there is an opportunity to address #41 and possibly #42 here as well (which I have not done in the code below)

safe_gets.c:

/*
 * Small modifications for using text_t interface by Steve Denson.
 * Super-simple text I/O for PropGCC, stripped of all stdio overhead.
 * Copyright (c) 2012, Ted Stefanik. Concept inspired by:
 *
 *     very simple printf, adapted from one written by me [Eric Smith]
 *     for the MiNT OS long ago
 *     placed in the public domain
 *       - Eric Smith
 *     Propeller specific adaptations
 *     Copyright (c) 2011 Parallax, Inc.
 *     Written by Eric R. Smith, Total Spectrum Software Inc.
 *
 * MIT licensed (see terms at end of file)
 */
#include <ctype.h>
#include "simpletext.h"

static volatile char _textScanTerminalCharEchoing = 1;

void scanEchoDisable()
{
  _textScanTerminalCharEchoing = 0;
}  

void scanEchoEnable()
{
  _textScanTerminalCharEchoing = 1;
}  

char* _safe_gets(text_t *text, char* origBuf, int count)
{
  char* buf = origBuf;
  while (count-- > 0)
  {
      int ch = text->rxChar(text);

      if (ch == 8 || ch == 127)
      {
          if (buf > origBuf)
          {
              if(_textScanTerminalCharEchoing)
              {
                text->txChar(text, '\010');
                text->txChar(text, ' ');
                text->txChar(text, '\010');
              }                
              count += 1;
              buf--;
          }
          count += 1;
          continue;
      }

      if(_textScanTerminalCharEchoing)
      {
        text->txChar(text, ch);
        if (ch == '\r')
            text->txChar(text, '\n');
      }            

      if (ch == '\r' || ch == '\n')
          break;

      *(buf++) = ch;
  }
  *buf = 0;

  return (origBuf);
}