Replace most invocations of fail keyword with die! macro
Remove fail keyword from lexer & parser and clean up remaining calls to
fail

Fix merge conflicts - Issue 4524
Merge remote-tracking branch 'nickdesaulniers/issue4524' into nocomm1
README.txt: Mention linenoise
Fix breakage
automated merge
README.md, mention curl not wget.
automated merge
Tweak the CONTRIBUTING.md file.
automated merge
check-fast fallout from removing export, r=burningtree
update compile-fail/map-types.rs to use hashmap
cat modernization (cleanup of a run-pass test)
remove old StdMap trait

this has been replaced by core::container::Map
rm commented out std::map code from json module

it was replaced by LinearMap
rename map -> oldmap and mark it as deprecated

LinearMap is quite a bit faster, and is fully owned/sendable without
requiring copies. The older std::map also doesn't use explicit self and
relies on mutable fields.