Change Framebuffer's containers/methods to improve performance.

* Reduce the size of Terminal::Cell.
* Change colors and attributes in Terminal::Rendition to bitfields/bitmask.
* Change Cells to use UTF-8 strings instead of vector<wchar_t>.  Store Rows in a vector instead of a deque.
* Add various Framebuffer::append() methods for more efficient passing of single and repeated characters.
* Change title/icon strings from deques to a vector typedef-- this is more for tidiness than any real performance.

src/terminal/terminaldisplayinit.cc

@@ -90,7 +90,7 @@ const char *Display::ti_str( const char *capname )
 }
 
 Display::Display( bool use_environment )
-  : has_ech( true ), has_bce( true ), has_title( true ), posterize_colors( false ), smcup( NULL ), rmcup( NULL )
+  : has_ech( true ), has_bce( true ), has_title( true ), posterize_colors( 0 ), smcup( NULL ), rmcup( NULL )
 {
   if ( use_environment ) {
     int errret = -2;