added all of SciTECO's declarations to the "SciTECO" namespace

normally, since SciTECO is not a library, this is not strictly
necessary since every library should use proper name prefixes
or namespaces for all global declarations to avoid name clashes.

However

 * you cannot always rely on that
 * Scintilla does violate the practice of using prefixes or namespaces.
   The public APIs are OK, but it does define global functions/methods,
   e.g. for "Document" that clashed with SciTECO's "TECODocument" class at
   link-time.
   Scintilla can put its definitions in a namespace, but this feature
   cannot be easily enabled without patching Scintilla.
 * a "SciTECO" namespace will be necessary if "SciTECO" is ever to be
   turned into a library. Even if this library will have only a C-linkage
   API, it must ensure it doesn't clutter the global namespace.

So the old "TECODocument" class was renamed back to "Document"
(SciTECO::Document).