Basic fromproj4 works, except need better handle when unprojected (longlat and latlong)

Also just need to expand to more projection name, datum name, and
ellipsoid name definitions, and also additional special parameters.

After that, test, and move onto from_wkt()...

pycrs/loader.py

@@ -0,0 +1,49 @@
+
+import json
+
+
+#################
+# USER FUNCTIONS
+#################
+
+# convenience methods for loading from different sources
+
+def from_url(url, format=None):
+    # first get string from url
+    # ...
+
+    # then load
+    if format:
+        # load string using specified format
+        pass
+    else:
+        from_unknown_text(string)
+
+def from_file(filepath):
+    if filepath.endswith(".prj"):
+        string = open(filepath, "r").read()
+        from_esri_wkt(string)
+    
+    elif filepath.endswith((".geojson",".json")):
+        crsinfo = json.load(filepath)["crs"]
+        
+        if crsinfo["type"] == "name":
+            string = crsinfo["properties"]["name"]
+            from_unknown_text(string)
+            
+        elif crsinfo["type"] == "link":
+            url = crsinfo["properties"]["name"]
+            type = crsinfo["properties"].get("type")
+            from_url(url, format=type)
+            
+        else: raise Exception("invalid geojson crs type: must be either name or link")
+
+    elif filepath.endswith((".tif",".tiff",".geotiff")):
+        pass
+        # ...
+
+
+
+
+                                      
+