Cleanup! Removed a bunch of stale FIXMEs.

* Cleaned up some comments.
* Removed some and tweaked some FIXMEs.
[Truffle] Options for inlining yield.
[Truffle] Option for making metaprogramming calls uncached.
[Truffle] Add option for using indirect calls for metaprogramming methods.
[Truffle] Try splitting all core methods by default.
Merge branch 'master' into truffle-head

Conflicts:
	core/src/main/java/org/jruby/truffle/nodes/dispatch/CachedBooleanDispatchNode.java
	core/src/main/java/org/jruby/truffle/nodes/dispatch/CachedBoxedDispatchNode.java
	core/src/main/java/org/jruby/truffle/nodes/dispatch/CachedBoxedMethodMissingDispatchNode.java
	core/src/main/java/org/jruby/truffle/nodes/dispatch/CachedBoxedSymbolDispatchNode.java
	core/src/main/java/org/jruby/truffle/nodes/yield/CachedYieldDispatchNode.java