Add matlab function to write IFOModel structure data to file

The output is intended to be identical to that of pygwinc.Struct.to_txt(),
useful for direct comparison.

matlab/write_struct.m

+% This write_struct function is intended to dump an IFO struct to a text file in
+% an identical format as dumped by the pygwinc.ifo.Struct().to_txt() method,
+% allowing for direct comparison between structs with e.g. diff.
+
+function write_struct(s, name)
+    if nargin == 2
+        fid = fopen(name, 'w');
+    else
+        fid = 1;
+    end
+
+    write_struct_fid(s, '', fid)
+
+    if fid ~= 1
+        fclose(fid);
+    end
+end
+
+
+function write_struct_fid(s, prefix, fid)
+    fields = sortrows(fieldnames(s));
+    for k = 1:length(fields)
+        field = fields{k};
+        o = s.(field);
+        if isempty(prefix)
+            p = field;
+        else
+            p = [prefix '.' field];
+        end
+        if isstruct(o)
+            if length(o) > 1
+                for i = 1:length(o)
+                    pp = [p '[' sprintf('%d', i-1) ']' ];
+                    write_struct_fid(o(i), pp, fid)
+                end
+            else
+                write_struct_fid(o, p, fid)
+            end
+        else
+            print(fid, p, o);
+        end
+    end
+end
+
+
+function print(fid, name, val)
+    if ischar(val)
+        val = sprintf('%s', val);
+    elseif isvector(val) && length(val) > 1
+        val = ['[' sprintf('%0.6e ', val) ']'];
+    elseif isnan(val)
+        val = 'nan';
+    else
+        val = sprintf('%0.6e', val);
+    end
+    fprintf(fid, '%s: %s\n', name, val);
+end