New formula: Asterisk 10

Adding a homebrew formula for Asterisk 10. There have been some attempts at this in the past, and it would be nice to see Asterisk back in homebrew. Please note, this is my first attempt at a Formula. THERE MAY BE ISSUES, `brew doctor` says this:

 * Trailing whitespace was found
 * Use "#{ENV.cc}" instead of hard-coding "gcc"
 * Use "#{ENV.cxx}" instead of hard-coding "g++"

At this point, if you have ideas how those messages can be fixed, I'll gladly try to implement them. Also, if you can test and provide feedback if this works on your system or if there are other issues that need to be addressed, that would be great as well.

Finally, I tried building this with Asterisk 11, but without `sudo` for `make install`, the pjsip stack wouldn't compile correctly.