change file extension of README from asciidoc to adoc
minor stylesheet tweaks

- force normal font weight on inline code
- set border-spacing to 0 for tables
fix styling of hr
resolves #29 add configuration for loading Ruby-based extensions

- allow GEM_PATH to be specified using --gem-path option
- allow requires to be specified using -r option
- fix spellings of AsciiDoc
- remove a few dead imports and options
Allow multiple occurrences of "-r" option.
Test for multiple occurrences of "-r" option.