Improved configuration & CLI

[pacmancoder]

To improve the usability of the emulator, the following configuration sources should be introduced:

• Global emulator configuration, used as the default for all files
• Per-asset (tap, sna, etc.) configuration for keeping asset-specific settings

These settings should be located in user-specific config folder (directories crate can be used)

Configuration sources should have the following priority (from the highest)

• Options specified in CLI
• Per-asset configuration
• Global configuration
• Emulator defaults

Additional change for this task will be CLI refactoring

Current commands related to starting emulator should be moved to run subcommand: rustzx run --tap jetpac.tap

Additional run subcommand args

--remember - save provided asset-specific settings

config subcommand

Subcommands:

• set - set global or asset-specific settings. Global options can be selected with --global flag
• defaults - reset asset settings for asset or globally.

Basically, part of run arguments should be moved to the different structopt structure and re-used for configuration commands