Fixes #215 - Real literal tests are broken for non-US locales

Run real and decimal literal tests with en-US locale.
Automatically include tests in reference test project.
Added Reference tests to build and project file.

The reference tests are now automatically built (on Windows) to prevent
accidental build errors in that project (as introduced in #204).

A RefTest target has been added to run the reference tests.

Minor restructuring of the project file.
Updated CONTRIBUTING since things are a bit easier now.
Merge pull request #216 from ygra/reference-tests

Some build system improvements to reference tests
Fix parsing of real literals on non-US locale.
Fix incorrect conversion of double in string on non-US locale.

Add tests for real literal output on non-US locales.
Merge pull request #217 from mrward/real-literal-different-locales

Real literals on different locales