Config files

[tomusdrw]

1. Loading ~/.parity/config.toml by default.
2. CLI option to specify config file --config
3. All config options are optional.
4. CLI parameters will always override config.
5. Docopt is no longer responsible for defaults (it wasn't possible to tell apart default value and CLI specified parameter) - flags are defined using a macro.

What might follow:
PR with "presets" - pre-defined config files for specific use cases.

Closes: #880

[tomusdrw]

I've tried tt muncher pattern here (so default and non-default fields could be mixed) but it's quickly reaching default recursion limit.

[coveralls]

Coverage increased (+0.2%) to 84.996% when pulling db59d9a on config-files into edcc408 on master.

[rphmeier]

Awesome! I can see this opening the door to nice presets for sure.

I'm not sure if keeping accounts to unlock + password files in the config is a good idea.
Also, is this file meant to be manually edited by the user to set defaults? Or is it updated automatically somewhere (I don't see it at first glance)

[tomusdrw]

The files that are included are just examples (and are used for tests).
User can manually crate this config file and provide one using --config CLI flag.

Defaults (our defaults) are still hardcoded - but no longer in Docopt, but rather in this usage! macro.

[rphmeier]

Is this intended to supersede #2014?

[tomusdrw]

Not really, afaict. #2014 specifies what auto means in some cases (like tracing, pruning). But in config you can use auto,on,off

[coveralls]

Coverage increased (+0.09%) to 84.901% when pulling 27d30fc on config-files into edcc408 on master.

[arkpar]

LGTM. Prefer someone else to take a look also

[tomusdrw]

Please have a look at parameters definition format - it's a bit different now, maybe someone will have a nice idea how to make it more pleasant.