Inlined `operator<<`s

This release fixes an issue where ConditionalOStreams can't be referenced in two translation units because the stream operators weren't inline.

Make mOStream a Constant Pointer

Changed the ostream pointer in ConditionalOStream a constant-pointer-to-ostream, so that it can't be changed while streaming is occurring.

std::ostream *const mOStream

First Release

The first release of conditional ostream! This contains a single header file with a simple std::ostream-like class that proxies a std::ostream instance, but avoids streaming operands if the stream is not set.