Added option parsing (issue #4).

* Moved utility functions into share/ruby-install/ruby-install.sh.
Auto-detect the md5sum utility (closes #12).
Allow using curl or wget (closes #7).
Moved auto-detection of wget/curl into auto_detect.

* Have auto_detect() define the download() function.
Updated the README.
Use lower case options.
Added Example commands.
Naming.
Removed the -c, --cflags option.
Use kramdown-man.
Updated the man page.
Updated the man pages
Fuzzy-match the output of the md5 checksum util (issue #12).
variables.sh was removed.
Strip the space after the ':'.
Removed duplicate logic.
Added tests for parse_options.
Regenerated the man page using kramdown-man 0.1.5.
Style.
Combined functions.sh into ruby-install.sh.