compiler: Document exception handling at the BEAM SSA level
compiler: Document exception handling at the BEAM SSA level

Document how exception handlers are structured at the the BEAM SSA
level. The material in this patch is based on an email conversation
between the author and Björn Gustavsson <bjorn@erlang.org>.

dgud/otp,bjorng/otp,jj1bdx/otp,potatosalad/otp,potatosalad/otp,dgud/otp,jj1bdx/otp,emacsmirror/erlang,g-andrade/otp,bjorng/otp,mikpe/otp,potatosalad/otp,getong/otp,emacsmirror/erlang,dgud/otp,potatosalad/otp,dumbbell/otp,vinoski/otp,vinoski/otp,erlang/otp,vinoski/otp,emacsmirror/erlang,isvilen/otp,dumbbell/otp,bjorng/otp,jj1bdx/otp,dumbbell/otp,isvilen/otp,rlipscombe/otp,vinoski/otp,g-andrade/otp,mikpe/otp,g-andrade/otp,vinoski/otp,bjorng/otp,erlang/otp,emacsmirror/erlang,rlipscombe/otp,dgud/otp,isvilen/otp,dgud/otp,emacsmirror/erlang,getong/otp,getong/otp,g-andrade/otp,isvilen/otp,emacsmirror/erlang,erlang/otp,getong/otp,mikpe/otp,potatosalad/otp,isvilen/otp,g-andrade/otp,emacsmirror/erlang,bjorng/otp,dumbbell/otp,jj1bdx/otp,rlipscombe/otp,isvilen/otp,vinoski/otp,bjorng/otp,dumbbell/otp,bjorng/otp,dumbbell/otp,dgud/otp,rlipscombe/otp,erlang/otp,erlang/otp,emacsmirror/erlang,dgud/otp,getong/otp,erlang/otp,rlipscombe/otp,mikpe/otp,isvilen/otp,emacsmirror/erlang,mikpe/otp,mikpe/otp,isvilen/otp,jj1bdx/otp,g-andrade/otp,erlang/otp,rlipscombe/otp,vinoski/otp,dumbbell/otp,bjorng/otp,getong/otp,potatosalad/otp,dgud/otp,rlipscombe/otp,dumbbell/otp,mikpe/otp,vinoski/otp,bjorng/otp,dumbbell/otp,isvilen/otp,getong/otp,rlipscombe/otp,jj1bdx/otp,jj1bdx/otp,dgud/otp,g-andrade/otp,g-andrade/otp,rlipscombe/otp,vinoski/otp,jj1bdx/otp,mikpe/otp,getong/otp,mikpe/otp,getong/otp,emacsmirror/erlang,jj1bdx/otp,dumbbell/otp,dgud/otp,bjorng/otp,rlipscombe/otp,potatosalad/otp,potatosalad/otp,g-andrade/otp,jj1bdx/otp,erlang/otp,isvilen/otp,potatosalad/otp,g-andrade/otp,erlang/otp,mikpe/otp,erlang/otp,vinoski/otp,potatosalad/otp,getong/otp