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

Fix clang example compilation

This reverts commit 6047e3ce.

Implemented feature as in #560 (ints/doubles as strings)

Fix #566 #568