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
vim: export is no longer a keyword
Merge remote-tracking branch 'nickdesaulniers/issue4524' into nocomm1
vim: add Self type
vim: unsafe:: namespaces were renamed to raw::
vim: 'be' is a reserved keyword
vim: use StorageClass for mut and const
vim: pub is just a plain old token keyword
README.txt: Mention linenoise
Fix breakage
automated merge
vim: 'fail' is no longer a keyword
README.md, mention curl not wget.
automated merge
Tweak the CONTRIBUTING.md file.
automated merge
check-fast fallout from removing export, r=burningtree
rustdoc: Remove definitions of spawn_listener and spawn_conversation
rustdoc: Fix some search-and-replace fallout