0.3.0: Add --top support

This release adds a --top flag. If you start px with --top, px will show a full
screen process listing updating every second.

The list is sorted by CPU time used by each process since "px --top" was
started.

Pressing "q" will make px exit --top mode.

Another way of entering --top mode is to make a symlink to px that ends in
"top". If px is started using that symlink it will do top mode even without the
--top flag.

0.2.2: Mostly polish

New / improved feature:
* Identify network socket based IPC on OS X

Fixes:
* Fix problems parsing CPU time strings like "1-19:31:31"
* Don't display ourselves or the ps we spawned
* Print warning about lsof potentially being slow
* Add GitHub URL to help message
* Fix an internal link in README.md

0.2.1: More details, better overview

* In the details view, list other processes started around the same time as the
current one.

* Add a column with the process name in it.

* Add column headings.

The difference from 0.2.0 is just a better formatted release message.

0.2.0: * Add a column with the process name in it

* Add column headings

* In the details view, list other processes started around the same time as the
current one.

0.1.0: First marketable release

This release adds a number of improvements compared to just running `ps`:
* List the most interesting processes last so you don't have to search or scroll
to find them
* Find processes by owner or command line by doing `ps chrome` or `ps root` (for
example)
* Print details about a given process using `px 1234`. Details include:
  * a process tree
  * a list of other processes this one is communicating with
  * a list of network connections