Please add license headers to source files

[pah]

In order to safely track the copyright origins of the source files, e.g. for inclusion in third-party libraries, the source files should carry individual license headers. Something like:

// This file is part of RapidJSON, a fast JSON parser/generator.
// http://miloyip.github.io/rapidjson
// 
// Copyright (C) 2011-2014 Milo Yip and all Contributors
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

Especially the optimized algorithms for itoa (#80) and dtoa (#97), which are based on third-party implementations, should mention their origins (and licenses, if different) correctly to avoid licensing issues.

[miloyip]

Agreed. I will do it.
Besides, I was thinking whether we should change tabs to space. But will this affect merging in different forks?

[pah]

I would certainly favour moving from tabs to spaces.

To simplify the merging, forks and open pull-requests should then perform the space changes locally as well. On the other hand, there is a "merge strategy" in git to allow ignoring such space changes.

[miloyip]

Done both in 0dbcc1c