Fix #594

Fix VC warnings

RawNumber Improvements / Clang Test Fix / Whitespace Cleanup

Later clang compilers will warn on float -> double promotion because it can add precision. In the context of RapidJSON – especially with its float methods on GenericValue – I think this warning holds no water and should be ignored.

Trim whitespace off the end of various lines.

Added an additional NumberStream specialization that will always perform a TakePush() even when just Take() is called. This supports RawNumber parsing by pushing onto our StackStream particular parts of the number that currently aren't captured because of full precision double parsing, such as the negative sign, scientific number exponents, etc.

RawNumber parsing fails with input streams that don't have copy optimization, such as the BasicIStreamWrapper stream. To work around this, instead do the Transcode copy operation by reading from a UTF8 StringStream instead of the original InputStream. Since the NumberStream downcasts all input Ch into chars, we know we're dealing with UTF8/ASCII compatible stack characters during the Transcoding.

Added optional support for trailing commas

This also fixes cases where the iterative parser should have produced
kParseErrorValueInvalid rather than kParseErrorUnspecifiedSyntaxError
when expecting a value (after a colon in an object, after a comma in an
array, and at the start of an array.)

This adds kParseTrailingCommasFlag to allow a trailing comma at the
end of maps and arrays. This is part of issue #36, adding optional
support for relaxed JSON syntax.

do potentially precision-losing conversions explicitly

Add PrettyWriter format option for writing array in single line.

This change adds PrettyWriter::SetFormatOptions with a corresponding
bitfield enum PrettyFormatOptions. This allows options affecting the
format of the PrettyWriter to be set. The first option to be provided
is kFormatSingleLineArray, which instructs the PrettyWriter to write
arrays on a single line, rather than breaking them up onto a line
per element.

[simplewriter.cpp] show generated output

This previously affects Writer:: SetMaxDecimalPlaces()

This makes it painfully obvious that writer expects subsequent key/value pairs.

Removed commented code and added an explanatory comment instead