diffable: Refactor command line flags handling
diffable: Refactor command line flags handling

Refactor command line parser to easily support flags with arguments,
NFC. This change is preparing the parser for a future patch which will
make it possible to pass arbitrary compiler options to compile:file/2
and compile:forms/2.

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