Consider using new TZM geo/geo-types

Would it make sense to migrate all internal postgis types to the proposed [geo-types](https://github.com/georust/geo/pull/797) that support T, Z, and M generic types? Are there any changes that should be made to that proposal? How should SRID be added to it? One option might be to double the number of types - e.g. `LineString`, `LineStringM`, `LineStringZ`, `LineStringZM`, `LineStringS`, `LineStringMS`, `LineStringZS`, `LineStringZMS`, where all of them are aliases to `pub struct LineStringTZM(...)` -- where SRID could be defined as either i32 or NoValue.

If SRID is not accepted to geo/geo-types as an i32 (which seems to be a postgis convention only), one option would be to have some sort of a wrapper enum as described in https://github.com/georust/wkt/issues/91 with an additional i32 srid.