Ghostscript.NET 1.1.2

Fixed GhostscriptPipedOutput.Data property get accesor in order to prevent a race condition. (thanks to "Marc Klenotic"). Added GhostscriptPipedOutput class as part of the Ghostscript.NET library. Fixed GhostscriptException error code text message resolving. Implemented better methods parameters checking and exception handling. Changed ImageMemoryHelper class from public to internal. Implemented opening files represented as MemoryStream from GhostscriptRasterizer and GhostscriptViewer. (that was some users request although there is no point of passing PDF as MemoryStream (or byte array) as it will anyway end up on the disk before it will be interpreted as PDF language, unlike the PostScript language, inherently requires random access to the file).