Implement setRadius (#55)

A projection may have a radius. This commit implements setRadius used in for example Equidistant Cylindrical where:
+R=<value> Radius of the sphere given in meters. As per documentation this function is applied on the end, so it takes precedence over +ellps.

Signed-off-by: Stefan de Konink <stefan@konink.de>

src/main/java/org/locationtech/proj4j/parser/Proj4Keyword.java

@@ -86,6 +86,7 @@ public static synchronized Set supportedParameters() {
             supportedParams.add(ellps);
             supportedParams.add(h);
 
+            supportedParams.add(R);
             supportedParams.add(R_A);
 
             supportedParams.add(k);

src/main/java/org/locationtech/proj4j/parser/Proj4Parser.java

@@ -156,6 +156,11 @@ private Projection parseProjection(Map params, Ellipsoid ellipsoid) {
         if (s != null)
             projection.setAxisOrder(s);
 
+        /* Radius of the sphere given in meters. If used in conjuction with +ellps +R takes precedence. */
+        s = (String) params.get(Proj4Keyword.R);
+        if (s != null)
+            projection.setRadius(Double.parseDouble(s));
+
         //TODO: implement some of these parameters ?
 
         // this must be done last, since behaviour depends on other params being set (eg +south)

src/main/java/org/locationtech/proj4j/proj/Projection.java

@@ -747,6 +747,10 @@ public Ellipsoid getEllipsoid() {
         return ellipsoid;
     }
 
+    public void setRadius(double radius) {
+        a = radius;
+    }
+
     /**
      * Returns the ESPG code for this projection, or 0 if unknown.
      */

src/test/java/org/locationtech/proj4j/CoordinateTransformTest.java

@@ -221,6 +221,11 @@ public void testPROJ4_LargeDiscrepancy() {
         checkTransformFromGeo("EPSG:29100", -53.0, 5.0, 5110899.06, 10552971.67, 4000);
     }
 
+    @Test
+    public void testRadius() {
+        checkTransformToWGS84("+title=long/lat:WGS84 +proj=eqc +R=57295779.5130823209", 1000000.0, 1000000.0, 1.0, 1.0, 0.01);
+    }
+
     @Ignore("TODO: Should these expect UnknownAuthoriyCode exceptions?") @Test
     public void XtestUndefined() {
         //runInverseTransform("EPSG:27492",    25260.493584, -9579.245052,    -7.84, 39.58);