Support --debug option for enabling Now CLI debug mode

[simonw]

This is really useful for seeing exactly what's going on.

$ datasette publish now2 covid.db --project=covid-cases
> [debug] [2020-04-07T05:01:50.253Z] Found config in file /private/var/folders/bl/5x847xbj2yb7xmp7f2tz7l280000gn/T/tmpbessv97g/datasette-now-v2/now.json
Now CLI 17.1.1
> [debug] [2020-04-07T05:01:50.263Z] user supplied a possible target for deployment
> [debug] [2020-04-07T05:01:50.264Z] Spinner invoked (Retrieving scope…) with a 1000ms delay
> [debug] [2020-04-07T05:01:50.264Z] Spinner ended (Retrieving scope…)
> [debug] [2020-04-07T05:01:50.280Z] GET https://api.zeit.co/www/user 
> [debug] [2020-04-07T05:01:50.788Z] GET https://api.zeit.co/www/user : 507.214ms
> [debug] [2020-04-07T05:01:50.840Z] Spinner invoked (Loading scopes…) with a 1000ms delay
> [debug] [2020-04-07T05:01:50.841Z] GET https://api.zeit.co/teams 
> [debug] [2020-04-07T05:01:51.332Z] GET https://api.zeit.co/teams : 490.462ms
(node:11348) Warning: No such label '> [debug] #1 GET /teams' for console.timeEnd()
> [debug] [2020-04-07T05:01:51.333Z] Spinner ended (Loading scopes…)
❗️  The `name` property in now.json is deprecated (https://zeit.ink/5F)
> [debug] [2020-04-07T05:01:51.334Z] Setting target to production
> [debug] [2020-04-07T05:01:51.335Z] Spinner invoked (Setting up project) with a 0ms delay
[now-client-debug] 2020-04-07T05:01:51.335Z Creating deployment...
[now-client-debug] 2020-04-07T05:01:51.335Z Provided 'path' is a directory. Reading subpaths... 
[now-client-debug] 2020-04-07T05:01:51.336Z Read 4 subpaths
[now-client-debug] 2020-04-07T05:01:51.337Z Found 1 rules in .nowignore
...