issue 5224
Update random.d

fix wrong usage in doc example (Random gen(unpredictableSeed)).
Update random.d

fixed spacing
fix Issue 10125 Unicode non-BMP decoding to dchar in stdio readln

strings were first decoded to wchars, each wchar was then separately
decoded to dchar, resulting in 2 dchars in the surrogate block instead
of 1 correct dchar.

added unit test to verify readln decoding of non-ASCII characters
Merge branch 'master' of github.com:D-Programming-Language/phobos into 5224
@blackwhale's review
@blackwhale's destruction
combine some statements
Implement issue# 10314.

This moves std.traits.unsigned to std.conv and adds std.conv.signed,
since for some reason, we have std.traits.unsigned but do not have
std.traits.signed.
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