cx16: added sys.waitirq() that just does a WAI like waitvsync() but it is explicit about its behavior

docs/source/_static/symboldumps/skeletons-cx16.txt

@@ -1,6 +1,6 @@
 
 Prog8 compiler v12.2-SNAPSHOT by Irmen de Jong (irmen@razorvine.net)
-Prerelease version from git commit d720eeae in branch master
+Prerelease version from git commit 3b687412 in branch master
 This software is licensed under the GNU GPL 3.0, see https://www.gnu.org/licenses/gpl.html
 
 Compiling program import-all-cx16.p8
@@ -1513,6 +1513,7 @@ sys  {
     set_rasterline  (uword line @AY) 
     update_rasterirq  (uword handler @AY, uword rasterpos @R0)  clobbers (A) 
     wait  (uword jiffies @AY)  clobbers (X) 
+    waitirq  () 
     waitrasterline  (uword line @AY) 
     waitvsync  () 
 }

docs/source/libraries.rst

@@ -1455,6 +1455,9 @@ miscellaneous
     If this is is not possible (for instance because your program is running its own irq handler logic *and* no longer calls
     the kernal's handler routine), you'll have to write your own wait routine instead.
 
+``waitirq ()``   (cx16 only)
+    efficiently wait until the next interrupt has occurred (any source). It uses the 65C02 'wai' instruction for this.
+
 ``waitvsync ()``
     busy wait till the next vsync has occurred (approximately), without depending on custom irq handling.
     can be used to avoid screen flicker/tearing when updating screen contents.

docs/source/todo.rst

@@ -17,6 +17,7 @@ Weird Heisenbug
 
 Future Things and Ideas
 ^^^^^^^^^^^^^^^^^^^^^^^
+- symboldump: some sort of javadocs generated from the p8 source files (instead of just the function signatures). Use markdown for formatting.
 - if floats are only used in constants and never end up as actual value for a variable or expression, don't complain about the "floats not enabled" if %option enable_floats is missing
 - why are (interned) strings stored as initialization value in the SymbolTable AND as string nodes in the interned string block? Something seems redundant here?
 - add @private to variables and subroutines declared in a scope to make them invisible from outside that scope?