small improvements

[keith-hall]

Hi,

Thanks for this useful wrapper library. I have updated the build instructions in the readme slightly, to make it easier to understand, and fixed the URL to Oniguruma.

I have also tweaked the console test program to accept (optional) arguments to tell it what regex and what text to match and which position to start from. If there are no arguments, it uses the original text and pattern, so it can be used exactly like it was before. I also changed it to output the capture group matches. I believe these changes help to make the application useful for making small manual tests of Onigmo without detracting from the original purpose of verifying that the Onigmo dll can be loaded.

In an attempt to make the API slightly easier to understand for newcomers, I also added some doc comments that were missing.