Added path related helper functions.

[tonious]

This patch adds two path related helper function.

OpenJsCad.Processor.setOpenJsCadPath( path );

This function allows the user to set a path to the OpenJsCad folder.

OpenJsCad.Processor.addLibrary( library );

This function allows users to import additional javascript files. Objects within those files can then be referenced within the OpenJsCad web worker context.

In both cases, paths can be relative or absolute.

The use case of both functions is to be able to add OpenJsCad as a git submodule, and allow use of OpenJsCad without necessarily forking OpenJsCad.

Both functions rely on the addition of an options hash to OpenJsCad.Processor. This hash is then passed through OpenJsCad.parseJsCadScriptASync. This involved changing the call parameters to add said hash.

This patch was inspired by iamwillhelms pull request1 but varies in syntax somewhat to better represent the actual goal of each function.

[tonious]

Example usage:

function onload()
{
  gProcessor = new OpenJsCad.Processor(document.getElementById("viewer"));
  gProcessor.setOpenJsCadPath( "OpenJsCad/" );
  gProcessor.addLibrary( "utils.js" );

  updateSolid();
}

[joostn]

Thanks!