Adding coapp definition

Adding usage comment at the top of the file for knowledge sharing

https://github.com/miloyip/rapidjson/pull/460#issuecomment-152232015

To create a nupkg, call CoApp's Write-NuGetPackage .\rapidjson.autopkg
-defines:MYVERSION=1.0.2 (or whatever version you want to call it)

Highlight main features in bold

Fixed typo

Add missing return statement, fix #448

Add break at default switch case statements fix #444

fix issue #444

Introduce comments support

* Comments parsing function correctly handles EOF.
* Since SkipWhitespaceAndComments can generate errors, its calls should be followed by RAPIDJSON_PARSE_ERROR_EARLY_RETURN macro.
* Some tests to make the bug never appear again.

<algorith> should be <algorithm>.

Might help some people see things better when skimming.

Keep Document value unchanged on parse error, fixes #437

Keeping the DOM unchanged in case of an error is the intended
behaviour according to the [documentation] [1].

Instead of forcing the value to `kNullType` before starting the
parsing, store the parsed value upon success via regular move.

[1]: https://miloyip.github.io/rapidjson/md_doc_dom.html#ParseError

Fix UB in GenericDocument::ParseStream

To check is it possible to expose allocator.

check return of fwrite to avoid warn_unused_result build failures. Fixed #420. Thank you.

Fix incorrect 64-bit alignment

Added unit tests for alignment macros.
Fixes #418

BigInteger: guard against self-assignment

Related-to: #404.
Suggested-by: @cosinekitty

doc: 自定义流应当使用 ParseStream 而不是 Parse

added missing fields of CMakeList.txt

this fixed cmake error for me

Implement = operator for BigInteger

There's a copy constructor, but no '=' operator implemented. This is dangerous.