A few scripts for dealing with README files from Github

Examples of usage:
- Render github flavored markdown to file:
  `ghmarkdown <markdown> > <file>`
  or
  `cat <markdown> | ghmarkdown > <file>`
- Render and open GFMd readme file for reading in console:
  `cat <markdown> | ghmarkdown | lynx -stdin`
  or
  `gfm <markdown_file>`