rustc: Fix formatting of env! error message

Death to caps.
syntax: Fix capitalization in macro_parser errors
Fix `rustpkg help` handling

In general, you could run "rustpkg help <cmd>" to see some specific
usage information for <cmd>.  However, this was handled in a very ad-hoc
and buggy manner.  For example, running "rustpkg help prefer" would
actually show you the usage information for the "uninstall" cmd.

This commit attempts to fix this by making Help a real Command, and
making the handing of it explicit.
define arch for iOS/ARM
Removed obsolete 'e' prefix on ty_evec and ty_estr.
Removed free_glue from tydesc (the code is still generated, but inlined in drop_glue).
Use the right type for self in methods and remove obsoleted items.
Fixes #7411, #10615.
"rustpkg prefer" should print the help for '"prefer" not "uninstall"
Various READMEs and docs cleanup

Noticeably closes #11428.
Trim src/ README, bring back version_info everywhere
Tighten up float literal lexing.

Specifically, dissallow setting the number base for every type of float
literal, not only those that contain the decimal point. This is in line with
the description in the manual.
Use target libraries instead of host libraries. Fixes #11243
Add /doc/rustuv to .gitignore
Removed remnants of `@mut` and `~mut` from comments and the type system.
doc: build the docs for librustpkg
Restore missing line breaks in doc/index.html

a30d61b05a removed all of the trailing whitespace in doc/index.md.
Unfortunately, that trailing whitespace was actually markdown syntax for
line breaks.
Add librustuv to doc/index.md
Add inline attributes documentation.

Closes #7959.
more backticks
Don't overwrite the options.output value from build_session_options