* Fixes

Version checking
Save contents of non-empty hashes
XSUB handling (both static and dynamic)
Avoid saving all the "bootstrap" subs for statically linked XSUB modules
sv_magic can do SvREFCNT_inc(obj) which messes up precalculated refcounts
allocation of XPV[INAHC]V structures needs fixing: Perl tries to free
them whereas the compiler expects them to be linked to a xpv[inahc]v_root
list the same as X[IPR]V structures.
ref counts
perl_parse replacement
fix cstring for long strings
shared globs (GV != EGV) for C backend
reload at runtime any .so that was used at compile-time
fix C block ends in B:CC for disconnected basic block trees
compile-time initialisation of AvARRAYs
signed/unsigned problems with NV (and IV?) initialisation and elsewhere?
CvOUTSIDE for ordinary subs
DATA filehandle for standalone Bytecode program (easy)
DATA filehandle for multiple bytecode-compiled modules (harder)
DATA filehandle for C-compiled program (yet harder)
Integrate C backend fixes into CC

* Features

compile time v. runtime initialisation
save PMOPs in compiled form
write C code to call pp_* directly
inline appropriate pp_*
selection of what to dump
snazzy command line invocation
options for cutting out line info etc.
comment output
shared constants
module dependencies

* Optimisations
filter out null ops
collapse LISTOPs to UNOPs or BASEOPs
compile-time qw(), constant subs
global analysis of variables, type hints etc.
copy-on-write and copy-on-grow SVs (may need extra tweaks to perl)
CSE?
demand-loaded bytecode (leader of each basic block replaced by an op
which loads in bytecode for its block)
