Added note about the mangler removing unneeded SRTs.
<ul>
<li>The code executed when a closure is entered is moved adjacent to
that closure's infotable. Moreover, the order of the info table
- entries is reversed.
+ entries is reversed. Also, SRT pointers are removed from closures that
+ don't need them (non-FUN, RET and THUNK ones).
<li>Function prologue and epilogue code is removed. (GHC generated code
manages its own stack and uses the system stack only for return
addresses and during calls to C code.)