[#61] Accept SRIDs as args to ST_Transform

[jesspav]

Currently, ST_Transform is only accepting utf8 args.
This change allows for SRIDs to be passed in as ints. It also adds some better argument checks.

Issue: #61

I tried going through a CRS and passing the to_json() output as the CRS args to the transform, but proj was failing to parse the json. I'll need to figure that out separately, but accepting the SRID seemed like a P0 issue, so fixing that first.

Testing

Unit tests and manual tests.

Examples

> SELECT ST_Transform(ST_SetSrid(ST_GeomFromText('POINT (1 1)'), 4326), 3857) as geom;
┌─────────────────────────────────────────────┐
│                     geom                    │
│                   geometry                  │
╞═════════════════════════════════════════════╡
│ POINT(111319.49079327357 111325.1428663851) │
└─────────────────────────────────────────────┘

> SELECT ST_Transform(ST_SetSrid(ST_GeomFromText('POINT (1 1)'), 4326), 'EPSG:3857') as geom;
┌─────────────────────────────────────────────┐
│                     geom                    │
│                   geometry                  │
╞═════════════════════════════════════════════╡
│ POINT(111319.49079327357 111325.1428663851) │
└─────────────────────────────────────────────┘

[paleolimbot]

but proj was failing to parse the json. I'll need to figure that out separately, but accepting the SRID seemed like a P0 issue, so fixing that first.

Agreed!

I think what's happening is that AuthorityCode::to_json() spits out "EPSG:1234" (with the quotes), and perhaps PROJ was expecting EPSG:1234 (no quotes). The way in this PR is great too!

[paleolimbot]

Thank you!