The `if` statement should have been a `for` loop, in order to allow recursively
sorting the subarrays with quicksort, and not resort to shell sort after
one step.
Additionally:
- Firm up PNG loader with some additional checks.
- Add helper functions to `core:image` to expand grayscale to RGB(A), and so on.
TODO: Possibly replace PNG's post-processing steps with calls to the new helper functions.
A package has canonically always been a directory, but odin allowing you to build a single-file package confused newcomers who didn't understand why they could then not access variables and procedures from another file in the same directory.
This change disallows building single-file packages by default, requiring the `-file` flag to acknowledge you understand the nuance.
`-help` for these commands also clarifies the difference.
```
W:\Odin>odin build -help
odin is a tool for managing Odin source code
Usage:
odin build [arguments]
build Compile directory of .odin files as an executable.
One must contain the program's entry point, all must be in the same package.
Use `-file` to build a single file instead.
Examples:
odin build . # Build package in current directory
odin build <dir> # Build package in <dir>
odin build filename.odin -file # Build single-file package, must contain entry point.
Flags
-file
Tells `odin build` to treat the given file as a self-contained package.
This means that `<dir>/a.odin` won't have access to `<dir>/b.odin`'s contents.
```
```
W:\Odin>odin run examples\demo\demo.odin
ERROR: `odin run` takes a package as its first argument.
Did you mean `odin run examples\demo\demo.odin -file`?
The `-file` flag tells it to treat a file as a self-contained package.
```
