irstv/H2GIS — pull request #75 by ebocher (2013-12-13 13:53:52+00:00)
Title: Add triangle analysis function

This PR adds 3 new functions for triangle.

```mysql
ST_TriangleSlope(GEOMETRY);
```
Compute the slope of a triangle in degrees

```mysql
ST_TriangleAspect(GEOMETRY);
```
Compute the aspect of a triangle Aspect represents the main slope direction angle compared to the north direction.

```mysql
ST_TriangleDirection(GEOMETRY);
```
Compute the main slope direction on a triangle represented by a linesegment