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/file_analysis/Manager.h

@@ -214,6 +214,12 @@ public:
 	 */
 	const char* GetAnalyzerName(int tag) const;
 
+	/**
+	 * Returns the enum type that corresponds to the script-level type
+	 * \c Files::Tag.
+	 */
+	EnumType* GetTagEnumType();
+
 protected:
 	friend class FileTimer;