Update the command matcher for the server command to log a more helpful
message when it's called without a subcommand.
Before:
```sh
$ target/debug/grin server
:: Some(ArgMatches { args: {}, subcommand: None, usage: Some("USAGE:\n grin server [OPTIONS] [SUBCOMMAND]") })
```
After:
```sh
$ target/debug/grin server
Subcommand required, use 'grin help server' for details
```
Unlike panic it doesn't call destructors (Drop) so all open transactions
are not closed. It's fine when LMDB file is open by the current process
only, but if another process keeps the same file open such transactions
will be considered alive until the second process exits. We usually have
one or more long-lived process (like `wallet listen`) which opens the
same wallet db as short-lived wallet commands. When a command fails it
calls process::exit and as result leaks a transaction.
This pr replaces such calls with an exit code return, which allows to call
all destructors before calling process::exit.
Fixes#1822
* Replace logging backend to flexi-logger and add log rotation
* Changed flexi_logger to log4rs
* Disable logging level filtering in Root logger
* Support different logging levels for file and stdout
* Don't log messages from modules other than Grin-related
* Fix formatting
* Place backed up compressed log copies into log file directory
* Increase default log file size to 16 MiB
* Add comment to config file on log_max_size option
* config file can now be generated by executable
* rustfmt
* remove now-unnecessary config defaults test
* set up paths and config file creation in user's home directory
* rustfmt
* remove default grin.toml
* add grin configuration command to spit out config file
* Split configuration into wallet and server
* rustfmt
* Restore logging to wallet configurations
* rustfmt
