Don't emit -fPIC for DMD on Windows. Fixes #166.
Fix "dub run" on OS X.

spawnProcess on OS X requires "./" to be appended for starting processes in the CWD.
The previous OSX fix is also needed for Linux, so change to version(Posix).
Move PlacementLocation to the proper module.
Fix ARM FP version identifiers.
Adjust style of dub.internal.vibecompat.data.json to latest vibe.d and use vibe.data.json if available.
Record the field name of JSON objects to improve error messages.
Let Json.checkType take an optional string to avoid compilation errors in the future.
Fix compiler error on DMD 2.063.2.
Add workaround for corrupted Json values when using Appender.
Improve the Appender workaround.
Fix warning that for some reason only occurs on some systems...