Improve st_buffer signature.
The user can now set specific buffer style parameters.
Fix st_buffer documentation and tests
Merge remote-tracking branch 'upstream/master' into erwan-merge

Conflicts:
	h2spatial/src/main/java/org/h2gis/h2spatial/internal/function/spatial/operators/ST_Buffer.java
	h2spatial/src/test/java/org/h2gis/h2spatial/SpatialFunctionTest.java
Remove newline characters
Merge pull request #254 from ebocher/st_bufferparameters

Improve st_buffer signature.

The user can now set specific buffer style parameters.

Supported signatures are

```mysql
SELECT ST_BUFFER('POINT(10 10)'::GEOMETRY, 20, 'quad_segs=8 endcap=round|flat|square join=round|mitre|bevel mitre_limit=5');
```

or

```mysql
SELECT ST_BUFFER('POINT(10 10)'::GEOMETRY, 20, 2);
```

It's similar to http://www.postgis.org/docs/ST_Buffer.html.

Fixes #97.