Support more robust determination of the executable location

[kitura]

Support more robust determination of the executable location

[tunniclm]

I have provided a PR #11 that implement both this and #12

[tunniclm]

The new tests I added fail on macOS because the executable is the test runner when you are running tests. These tests fail with the old way of getting the executable as well.

I will see if there's a way to fix that, or else I can remove the test. Either way this method of finding the executable is no worse than before in this respect, and better in the ways noted above.

[tunniclm]

I have added 2 more PRs, based on #11

• #14 - adds a test program that is executed to test loading works outside XCTest runner (to test what happens in a real application, rather than just in tests)
• #15 - adds a modification that makes loading work inside XCTest runner (which fixes the new tests failing on macOS, plus allows exe and project relative config loading to work from tests)

[tunniclm]

NOTE: the merge order matters here. For example, If we want all 3 PRs, then the merge order would be:

• #14 (merging test program into the #11 PR)
• #15 (merging XCTest runnner support into #11 PR)
• #11 (merging .project and robustness + test program + XCTest runner support into master)

[youming-lin]

Closed by PR #16.