Improved reader

[dundalek]

We use built-in clojure reader to parse the command mode, but it does not accept some shell forms.

Possible approaches:

1. Try to hack the current reader to accept those forms (this would be my favorite if possible).
2. Build the parse for command mode, then hand the forms in clojure code the built-in reader (probably a way to go).

Interesting inspiration might be Racket, since it is so flexible defining new languages.

Current limitations I am aware of:

• IP addresses (invalid number error)
  replace ping 8.8.8.8
  with ping "8.8.8.8"
• unquoted brace expansion (gets parsed as symbol and a map)
  replace ls *.{cljc,clj}
  with ls (expand "*.{cljc,clj}")
• tilde with slash
  e.g. vim ~/.closhrc
• at sign, tries to deref var e.g. git clone git@github.com:dundalek/closh.git
• multiple variable expansion, e.g. echo $USER/$DISPLAY