Enable wrapping of variables in the variables view

I also added an option for this, which made it easier for me to debug.
I haven't added it to the prefs yet.

TODO:

- Add the option to the prefs.

- Allow to turn on wrapping on a per-variable basis ('w' will turn this
  on and off in the variables,   view, and there will also be an option
  in the variable inspection options window).

- Right now, wrapped lines beyond the first line are indented two
  spaces.  This is the same as what digging into a variable looks like,
  which make it confusing (granted, digging in still indents further,
  but it's harder to follow).  I think variables that are sub variables
  should have some kind of character preceding them, like:

    varname: [1, 2, 3]
    + 0: 1
    + 1: 2
    + 2: 3

- When variables are not wrapped, there should be an ellipses at the
  end.  When unicode is supported, we can use …, otherwise, we use ...
Add variable wrapping to the prefs
Remove 200 character limit on strings in the variables view

If someone wants to limit the length of the string, he should write a
custom stringifier to do it.
Fix * shortcut for displaying of private members in expanded vars view
Add w shortcut for toggling wrapping in the variables view
Fix a bug where boolean settings set to True were set to "True"
Add a checkbox for wrapping to the Variable Inspection Options window
Print ellipsis at the end of an overlong unwrapped variable

This was supposed to use the unicode ellipsis (…) when possible, but
this does not work.  The behavior is very strange.  If you replace the
last character with …, it puts a ?.  If you replace the second to last
character, it replaces that *and* the last character with a ?.  If you
replace the third to last character, it works.  Therefore, for now, we
always just use ... (three dots) regardless of the console encoding.
Make "| " the prefix before nested variables

I've factored this out into a single variable so that it's easy to
change to something else if you don't like it.
Update custom stringifier example with a method to use sub-second timeouts
Update run_with_timeout docstring
Merge pull request #21 from asmeurer/stringifier-update

Update custom stringifier example with a method to use sub-second timeout
Make sure current stack frame is always visible.
Merge branch 'wrap-from-aaron'
Add version history entry for line wrap.
Don't crash on 'delete' command to empty breakpoint window.
Bump urwid version. Add README to MANIFEST.in.
Bump version.
Change docs for 'L', suggested by Joachim Durchholz.
Make sure users get that the help is scrollable.