Add an option for the Visvalingam simplification algorithm (#16)

* First attempt at porting Paul Mach's Visvalingam implementation

* Make indent

* Mostly working

* Approximate equivalence from Douglas-Peucker to Visvalingam levels

* Don't simplify away tile boundary crossing points

* Add a command-line option and test for Visvalingam simplification

* Update changelog

* Cleanup in response to review feedback

* Include <stdio.h> to fix compiler warnings

man/tippecanoe.1

@@ -35,7 +35,7 @@ For this fork you will need to build from the source repository:
 .PP
 .RS
 .nf
-$ git clone https://github.com/protomaps/tippecanoe.git
+$ git clone https://github.com/felt/tippecanoe.git
 $ cd tippecanoe
 $ make \-j
 $ make install
@@ -616,6 +616,8 @@ the line or polygon within one tile unit of its proper location. You can probabl
 \fB\fC\-pt\fR or \fB\fC\-\-no\-tiny\-polygon\-reduction\fR: Don't combine the area of very small polygons into small squares that represent their combined area.
 .IP \(bu 2
 \fB\fC\-\-tiny\-polygon\-size=\fR\fIsize\fP: Use the specified \fIsize\fP for tiny polygons instead of the default 2. Anything above 6 or so will lead to visible artifacts with the default tile detail.
+.IP \(bu 2
+\fB\fC\-av\fR or \fB\fC\-\-visvalingam\fR: Use Visvalingam's simplification algorithm rather than Douglas\-Peucker's.
 .RE
 .SS Attempts to improve shared polygon boundaries
 .RS