Fix std.traits for large input

std.traits: EnumMembers, isExpressionTuple, isTypeTuple & Largest balks
at large input
EnumMembers now works with single-member enums.
fix Issue 10230 - Duplicated buttons for runnable examples
Add README

A must for good Github repos
Add Contribution Guidelines

Github will "add a link to your file when a contributor creates
an Issue or opens a Pull Request".
https://github.com/blog/1184-contributing-guidelines
do reverse of a bytecode in lookbehinds
backtracking matcher works with reversed bytecode
ditto with Thompson matcher
cleanup to keep lookahead/lookbehind more in sync for future

Fix 64 bit issues, remove useless debug hook
Made unix domain sockets work on Linux.
Made the fix apply to all unices and added a unit test.
fix broken indention, detab
Fix issue 10874.

Don't assume that is(A : B) means a==b is valid, or that !is(A : B)
implies that a==b is invalid. Instead, test for a==b explicitly.

More specifically, int and ulong are ==-comparable, even though ulong is
not implicitly convertible to int. Thus, one should be able to convert
ulong to an int-based enum, but is(A : B) in the signature constraint
prohibits this. Testing for a==b explicitly, OTOH, makes this work.
It appears that whoever changed the name of the range parameter to encode didn't rename the parameter everywhere in the function.
Add unittest for issue 6893.
Allow narrowing conversions of enum -> integral (int, short, etc.).

It will just throw at runtime if the value of the enum is too large.
Add unittest for narrowing enum -> integral conversions.
Mark std.string.chop and its unittest as @safe and pure
Mark leftJustify, rightJustify and center as pure
Mark std.string.inPattern as @safe and pure