Support import of various fixed-width formats.

This supports reading: SPSv1, SPSv2.1, P190 and custom
fixed-width formats. Supports skipping lines by startswith()
matching or by complete match (e.g., "EOF").

Closes #300 (SPS v1)
Closes #301 (SPS v2.1)
Closes #302 (P1/90)

bin/preplots.py

@@ -1,15 +1,33 @@
-import legacy_fwr
+import fwr
 
 """
 Preplot importing functions.
 """
 
 def from_file (file, realpath = None):
+	"""
+	Return a list of dicts, where each dict has the structure:
+		{
+			"line_name": <int>,
+			"points": [
+				{
+					"line_name": <int>,
+					"point_number": <int>,
+					"easting": <float>,
+					"northing": <float>
+				},
+				…
+			]
+		}
+	On error, return a string describing the error condition.
+	"""
+
 	filepath = realpath or file["path"]
-	if not "type" in file or file["type"] == "sps":
-		records = legacy_fwr.from_file(filepath, file["format"] if "format" in file else None )
-	else:
-		return "Not an SPS file"
+	records = fwr.from_file(filepath, file)
+
+	if type(records) == str:
+		# This is an error message
+		return records
 
 	lines = []
 	line_names = set([r["line_name"] for r in records])