Remove $s in README.md's terminal commands

These make it tedious to enter them all, as each line needs to be copied
one by one.
Merge pull request #104 from iirelu/fix-readme-commands

Remove $s in README.md's terminal commands
Went through and fixed small PEP-8 errors

Anything that showed up less than 10 times when running `pep8 --count`,
I fixed. This includes all instances of E112, E113, E124, E222, E272,
E502, E502, E703, E711, E713, E714, E721, and W601.
Purged trailing whitespace

For compliance with PEP-8 W291 and W293.
Corrected small error

Underscores and underlines look really similar.
Fixed horrifyingly bad indent errors

3/5 space indented code. *Shudders*.
Got rid of obsolete error raising syntax

`raise x, y` is obsolete. PEP-8 warning W602.