Use TOML for the configuration file

[WhyNotHugo]

Use TOML as a config format:

• TOML is clearer than our current config format, unambiguous, and other pros I believe we already know.
• It may be a bit premature though, since the current format hasn't given any problems.
• TOML is becoming a lot more popular, especially in the python community.

Set default values when we load the config, rather than scatter them around the app, which should make everything a bit cleaner.

Closes #31

[WhyNotHugo]

@untitaker I'd love some feedback on whether this is worthwhile. Not sure it's of any actual use, though it makes sense for have todoman and vdirsyncer use the same format.

[untitaker]

I am really not sure whether adding a new dependency is worth it if you currently have two config keys, both of which are strings.

Switch to TOML won't happen that soon for vdirsyncer. The intermediate goal in vdirsyncer's case is to get everybody to switch to quoted strings in their config.

[untitaker]

If you're adding dependencies already you might as well use JSON-Schema for this

[WhyNotHugo]

Huh, yeah, I'll look at validating the config file, since that would be a stronger bonus. But I don't see how to do this without another dependency (python-jsonschema).

[WhyNotHugo]

Added schema validation, and some tests. I believe we can also clean up a few other bits of code, since we can always assume that all configuration variables exist, and are valid.

[untitaker]

Implementation looks good to me. This adds 0.1s overhead on my machine though.

[untitaker]

Oh, I see that you're using toml, I'd rather recommend pytoml. Its code quality is better.

[WhyNotHugo]

I'd rather recommend pytoml

I'll take a look at it. The interface seems pretty much the same.

[untitaker]

Yeah the interface is always json-ish. But toml.loads is 230 lines.

[WhyNotHugo]

I've opted for configobj (#31) rather than toml.

• ini works well enough for us.
• Making users change their config file is a downside.
• Errors for pytoml are rather unfriendly (See Tab in string yielding error avakar/pytoml#5)
• The validation schema syntax for JSON (which is what's used here) is horrible.
• One extra dependency vs two extra dependencies.