Add flags to copy command

[stevesims]

The copy command currently only takes a source and destination path, and has its limitations.

It would be useful to add in some more options, and to have them enabled/disabled via flags on the command.

Output when copying multiple files from the CLI is always "verbose" - if the copy command is being used via mos_oscli it may be useful to be able to negate this behaviour. This would be a "silent" flag.

Copying directories is not supported, or copying directories that match a source pattern. We may wish to consider adding support for a "recursive" copy flag.

As noted in #55 the copy command prevent files from being overwritten. Ideally instead we should ask permission to overwrite files. A "force" flag could allow overwrites to automatically be confirmed. If the "silent" flag is set, and "force" is not set, then the command should probably just pass by those files.

The copy command currently always has visibility of all files, including hidden and system files. We may wish to change this behaviour, and add flags to allow hidden/system files to be seen and copied.

When copying files, currently attributes are not preserved. It may be useful to change this behaviour, with flags to control whether attributes will be copied or not.

[stevesims]

the mos_copy API is written to only use two registers, one for source, the other for destination. it calls through to the same underlying copy function as the CLI, but sets it in a "non-verbose" mode. as no "flags" byte was designed into that API call, we can't add one now and maintain compatibility

whilst we could add in a mos_copy_with_flags API, it may be simpler instead to just advise the use of mos_oscli

the down-side of that approach is that the command string needs to be constructed, and care taken when doing so. this means ensuring the command is prefixed with a % to ensure alias resolution is skipped, and filenames that have spaces are wrapped in double-quotes. an API that accepts a flags byte would be significantly easier to use, as filename arguments in APIs already understand spaces so no double-quote wrapping is needed

[stevesims]

a valid approach for a more sophisticated copy command could be to implement such a command via a moslet. one could then set up an alias for copy to use the moslet instead of the inbuilt copy command

whilst it's tempting to enhance the current command to add support for flags, doing so would increase the size of MOS and our available ROM space is tight. there are likely other features that would be more useful to add