Switched away from sprintf, which is prone to buffer overflows.

Most reasonable platforms have this function. If you're here because
this broke the build for you, consider adding an ifdef for your platform
and using sprintf there (but not on other platforms).

git-svn-id: http://svn.code.sf.net/p/jsoncpp/code/trunk/jsoncpp@269 1f120ed1-78a5-a849-adca-83f0a9e25bb6
Added further floating point tests.

git-svn-id: http://svn.code.sf.net/p/jsoncpp/code/trunk/jsoncpp@270 1f120ed1-78a5-a849-adca-83f0a9e25bb6
Added more floating point tests.

The first demonstrates a bug that I will soon fix.

git-svn-id: http://svn.code.sf.net/p/jsoncpp/code/trunk/jsoncpp@271 1f120ed1-78a5-a849-adca-83f0a9e25bb6
Replaced the complex implementation of valueToString(double).

The previous one was confusing and prone to buffer overflows, and didn't
work correctly with 16-decimal-digit numbers. The new one simply uses
snprintf with a standard format string.

The major change is that we don't always print a decimal point now.
Fortunately, JSON doesn't distinguish between integers and reals.

git-svn-id: http://svn.code.sf.net/p/jsoncpp/code/trunk/jsoncpp@272 1f120ed1-78a5-a849-adca-83f0a9e25bb6
Updated two calls to sprintf that I missed in r269.

git-svn-id: http://svn.code.sf.net/p/jsoncpp/code/trunk/jsoncpp@273 1f120ed1-78a5-a849-adca-83f0a9e25bb6
Fixed some snprintf-related build breakages in Visual Studio.

git-svn-id: http://svn.code.sf.net/p/jsoncpp/code/trunk/jsoncpp@274 1f120ed1-78a5-a849-adca-83f0a9e25bb6
Update README, .gitignore, and .travis.yml files