Fix various documentation, mostly related to file analysis.

- Fix examples/references in the file analysis how-to/usage doc.

- Add Broxygen-generated docs for file analyzer plugins.

- Break FTP::Info type declaration out in to its own file to get
  rid of some circular dependencies (between s/b/p/ftp/main and
  s/b/p/ftp/utils).

src/BroDoc.h

@@ -413,4 +413,10 @@ private:
  */
 void CreateProtoAnalyzerDoc(const char* filename);
 
+/**
+ * Writes out plugin index documentation for all file analyzer plugins.
+ * @param filename the name of the file to write.
+ */
+void CreateFileAnalyzerDoc(const char* filename);
+
 #endif