Removing '$ ' from each line of input before executing code blocks

[jonocodes]

To address #11

This does not take care of the root user case which starts lines with '# ' since I thought those might get confused with shell comments.

Here is the input markdown I used to try with it.

$ echo hello 1

$echo hello 2

 $  echo hello 3

$ echo line 1
$ echo line 2
 $ echo line 3
  $ echo line 4
 $  echo line 5
echo line 6