Add a filetype plugin for ca65.

ftplugin/asm_ca65.vim

@@ -0,0 +1,17 @@
+" Vim filetype plugin file
+" Language:     CA65 Assembler for 6502 Architectures
+" Maintainer:   Max Bane <max.bane@gmail.com>
+
+if exists("b:did_ftplugin") | finish | endif
+let b:did_ftplugin = 1
+let s:keepcpo= &cpo
+set cpo&vim
+
+setlocal include=^\\s*\\.\\(include\\\|incbin\\\\|macpack\\)
+setlocal comments=b:;
+setlocal commentstring=;\ %s
+setlocal formatoptions+=ro
+set wildignore+=*.o
+
+let &cpo = s:keepcpo
+unlet s:keepcpo