Resolve various deprecation warnings.

[jverkoey]

• fileName -> fileURL
• NSFullScreenWindowMask -> NSWindowStyleMaskFullScreen
• NSFileHandlingPanelOKButton -> NSModalResponseOK
• NSPNGFileType -> NSBitmapImageFileTypePNG

TODO

• Revert the nil comparison changes.

Pre-work for #324

[LIJI32]

Two of these warnings are conscious design and style choices:

• The use of filenames over URL: While long deprecated, the NSString based APIs are cleaner than the NSURL based alternatives, as NSURL doesn't provide any benefits while requiring lengthy conversions between NSURL and NSString.
• Implicit conversion between pointers and bools is a style choice; since when did that even become a warning?

As for the rest – good catches, I never remember which of these symbols are the non-deprecated ones.

[jverkoey]

Implicit conversion between pointers and bools is a style choice; since when did that even become a warning?

Ah this is a style habit for me from the Google Objective-C style guide; I don't feel strongly about it here though because we're not interacting with BOOL, so am happy to revert that change. I'll add a TODO to the PR description.

[jverkoey]

The use of filenames over URL: While long deprecated, the NSString based APIs are cleaner than the NSURL based alternatives, as NSURL doesn't provide any benefits while requiring lengthy conversions between NSURL and NSString.

Agreed the string-based APIs had historically provided better facilities for working with paths. macOS 10.6 (~2016, roughly around the time you started this repo) introduced new APIs on NSURL for working with paths, so in many cases the APIs are comparable now.

[[self.fileName stringByDeletingPathExtension] stringByAppendingPathExtension:@"ram"]

becomes

[[self.fileURL URLByDeletingPathExtension] URLByAppendingPathExtension:@"ram"].path

The need to invoke path to convert to a string can be made less obtrusive by using property notation, and I've also made the UTF8String invocations follow a similar pattern (from [self.fileName UTF8String] to self.fileURL.path.UTF8String which is intended to improve readability by removing a layer of [ ] brackets.

I'm leaning toward resolving the deprecation warnings for this, but if you feel strongly about keeping the deprecated APIs in place I will defer to your call and can revert the fileName changes if desired.

[jverkoey]

Changes to nil checks have been reverted.

[jverkoey]

Another proposal for the fileName -> fileURL change is that I'd be happy to make a helper method for changing the file's extension if clarity / verboseness is the primary concern.