DDoc fixes

This fixes some warnings as identified by the compiler,
as well as some broken cross-reference links caused by
DDoc auto-formatting of the current symbol.
Merge pull request #1820 from CyberShadow/ddoc-syntax-fixes-6

DDoc fixes
std.stdio: Fix DDoc syntax in thrown exception documentation

Introduced in 402af9d0c400cb1f47d4b2b6e16bfac6b875fbd6
Merge pull request #1821 from CyberShadow/ddoc-syntax-fixes-7

std.stdio: Fix DDoc syntax in thrown exception documentation