* introduce a new Connections object to track all positional strings
passed as the CLI arguments
* each tile provider can now indicate if it can take a positional CLI
arg, and if the value can be shared between multiple providers, i.e. if
its a directory that could contain files for multiple providers
* make xyz use better types - u8 for zoom, u32 for x&y. Postgres casts
those to INT2 and INT8
* minor bug in pre-push git hook to abort in case of a testingerror
* added GIF detection/type
* combine MVT and compression concepts into one enum more explicitly. It
is not ideal (technically they are separate concerns), but it keeps it a
bit simpler for now for multiple providers.
* set content encoding and content type on HTTP responses if known, and
also include them in the `/catalog` response (json)
* raise an error if the user attempts to merge non-concatenatable tiles
from multiple sources. We may want to implement it in the future, e.g.
combine multiple semi-transparent PNGs. Or even combine GIF & PNG & JPEG
* do not set content-type on empty responses (http 204)
* add tilejson outputs to testing
* NEW: support for #512 - pg table/function auto-discovery
* can filter schemas
* can use patterns like `{schema}.{table}.{column}` and
`{schema}.{function}`
* NEW: add `disable_bounds` bool flag to allow disabling of the bounds
computation
* reworked integration tests to use yaml
