This PR includes georust#772 and georust#812

---

This PR focuses on `geo-types` only. This is a part of georust#742.

This PR changes the underlying geo-type data structures to support 3D data and measurement values (M and Z values). The PR attempts to cause relatively minor disruptions to the existing users (see breaking changes below). My knowledge of the actual geo algorithms is limited, so please ping me for any specific algo change.

## geo-types restructuring
All geo type structs have been renamed from `Foo<T>(...)` to `Foo<T, Z=NoValue, M=NoValue>(...)`, and several type aliases were added:

```rust
// old
pub struct LineString<T: CoordNum>(pub Vec<Coordinate<T>>);

// new
pub struct LineString<T: CoordNum, Z: ZCoord=NoValue, M: Measure=NoValue>(pub Vec<Coordinate<T, Z, M>>);

pub type LineStringM<T, M=T> = LineString<T, NoValue, M>;
pub type LineString3D<T> = LineString<T, T, NoValue>;
pub type LineString3DM<T, M=T> = LineString<T, T, M>;
```

## NoValue magic
`NoValue` is an empty struct that behaves just like a number. It supports all math and comparison operations. This means that a `Z` or `M` value can be manipulated without checking if it is actually there.  This code works for Z and M being either a number or a NoValue:

```rust
pub struct NoValue;

impl<T: CoordNum, Z: ZCoord, M: Measure> Sub for Coordinate<T, Z, M> {
    type Output = Self;

    fn sub(self, rhs: Self) -> Self {
        coord! {
            x: self.x - rhs.x,
            y: self.y - rhs.y,
            z: self.z - rhs.z,
            m: self.m - rhs.m,
        }
    }
}
```

## Variant algorithm implementations
Function implementations can keep just the original 2D `<T>` variant, or add support for 3D `<Z>` and/or the Measure `<M>`. The above example works for all combinations of objects. This function only works for 2D objects with and without the Measure.

```rust
impl<T: CoordNum, M: Measure> Line<T, NoValue, M> {
    /// Calculate the slope (Δy/Δx).
    pub fn slope(&self) -> T {
        self.dy() / self.dx()
    }
}
```

## Breaking changes
* It is no longer possible to create Coordinate with just `x` and `y` values using implicit tuple constructor. Use `coord!` instead.

This simplifies the design a bit, by using the same `CoordNum` everywhere. `NoValue` can now be used anywhere, making it possible to define `Coordinate<NoValue>` -- an empty value.

Co-authored-by: Corey Farwell <coreyf@rwell.org>