rename, export, and document low-level DER functions
added Tag type, tricks
simplify encoder/decoder hooks: eliminate type arg
small intro wording improvements
improve type docs, change Racket values for set/sequence-of
don't export define-asn1-type... TODO: replace?
... changing way hooks work
... done with encode, added wrap type
... decoder hooks, removed type:defined
... add Wrap form
turned macros into functions when possible
... restored delay type as Delay
... hooks, docs
rename DER-frame p/c field to tagkind
add bit-string, fix boolean
document Delay, add bib
improve ANY docs
docs on eg INSTANCE OF types
added todo
pkcs1 example, standalone