Fix trivial nitpicks
[Refactoring] Delaying throwing Exception makes control flow analysis simple
[Refactoring] Define enforceFmt
fix Issue 10254 - Purity correctness is broken with constructor
[appender] Reuse ensureAddable for reserve implementation

AFAICS, they have mostly same code.
[appender] Accepting qualified buffer is not safe behavior

To reduce existing code breaking, mark such construction as @system.
[appender] Determine @trusted operations
[parse, str.to!x] Determine @trusted operations
[formatValue] (bool, null, integrals, floatings, chars)

Floating point is blocked by sprintf
[non to!string] because they are unrelated to formatValue
[format] Add @safe/pure ability to writeUpToNextSpec, fillUp, and formattedWrite
[formatValue] (pointer)

+ Infer attributes in retro range primitives
[to!string] severals
[appender] Mark pointer slicing @trusted (fix for issue 10359)
Merge pull request #1337 from 9rnsr/fix_attrs

Potentially @safe & pure formatting
Replace std.uni in phobos with new version

Fixes some issues in std.string and std.json
adds workarounds to make it work with current DMD

Also add to{Lower,Upper}InPlace, and other minor enhancements since review
few tweaks to aid std.string/std.uni symbiosi:s
fixup 64bit unittest
debuging prints for auto-tester
remove misleading comment