Add a command to list all commands via the LLDB command interface.

[mrhappyasthma]

The README has the list of commands, but it would be useful if there was a command to list all commands.

E.g.

listcommands

pvc - Print view controller hierarchy
> pv - Print view hierarchy
... Etc.

[mrhappyasthma]

Turns out the commands are listed by default in help command. But I need to add docstrings so that they get parsed correctly.

[mrhappyasthma]

It's a lot better now as of 23682b3

However I can't figure out how to adjust the Syntax: part of the help text that appears to be autogenerated:

For example:

(lldb) help ivars
     Prints out all the ivars of an object.  Expects 'raw' input (see 'help
     raw-input'.)

Syntax: ivars
Print out all the ivars of an object.

  NOTE: The parsing of the ivar type encoding is very hacky, but it should
         be sufficient for most cases. Therefore the resulting list may have
         mistakes or could be missing some ivars whose type could not be
         parsed.

  Usage:
    ivars <instance>

The part of the above snippet: Syntax: ivars is autogenerated. And I cannot figure out how to have it list the parameter(s) taken. As a workaround, I manually append Usage: ivars <instance> to the bottom of the help text.

It's not ideal, but sufficient for now.