Update to ARC
Use Foundation (Core) data types
Use Objective-C literals
Remove mention of Carbon
Use new APIs for reading/writing plists

The previous APIs were deprecated because they do not follow proper Cocoa memory management rules.
Do not use the C++ `not` operator
Remove unused `resultCode = 0` assignment

We could make this more terse by returning early, but the surrounding methods all share a similar style.
Remove dead code for sheets

At this point, if we decide to add support for sheets based alerts (nibs) we should add it to the newer Dialog2 plugin.

Along this same line, remove the commented text describing the usage for sheets too.
Fix return code from tm_dialog

Two places didn’t set res to EX_OK even though there was no error.

I changed the default return value from -1 to EX_USAGE. Ideally we would be more specific.
Introduce -h/--help for tm_dialog (1.x)

Unlike unknown options, here we print the help text to stdout and return EX_OK.
Add deprecation warning