Added multithreading to BinaryArithmetic to increase speed.

[KingAkeem]

This PR references issue #21 I've added multithreading code for concurrently running four strip_leading_zeroes functions. This has reduced the test time of the BinaryArithemetic tests by 3x as much. I've attached some photos of comparison below:
Before multithreading:

After multithreading:

[faheel]

This is great! Can you also take a look at other places where multithreading can be used to speed up things? For example, calculating prod_high, prod_mid and prod_low on different threads may lead to a significant speedup.

[KingAkeem]

Thank you! I definitely was planning on it. I just wanted to get a review on what I had already done to show the improvement and let you know that I was working on it.

[KingAkeem]

I attempted to add more threads for calculating prod variables and it seems that there is a bottleneck when it comes to spawning threads. After the first 4, the overhead cost of spawning threads causes a decrease in speed.

[faheel]

Just a small change and then it'll be good to merge.

[faheel]

The threads t1, t2, ... aren't very descriptive and should be renamed to thread1, thread2, ...

[KingAkeem]

Added the fix :)

[faheel]

@KingAkeem I've updated the testing and build mechanism recently, so can you merge the recent changes to your branch and push it again to that we can if the build still fails (only 1 build, that uses GCC 8 and does coverage analysis should fail, the rest should pass).

[faheel]

@KingAkeem Please merge with latest upstream (for the reason mentioned above)

[KingAkeem]

@faheel I've merged the recent changes and pushed the branch. Sorry about taking so long, I just saw your comment.

[faheel]

Looks like on Linux we'll need to add -pthread when compiling to link the pthread library. It's not that big of a deal, but then the compilation step will require special attention from the user which impacts the main features of this library, which are simplicity and ease of use. So I'll need to think about this and see what's the best thing to do here.

What are your thoughts on this @KingAkeem?

[KingAkeem]

@faheel Is there no way to add the -pthread library in the release script? But we're going to have to have to use some library to provide us with the ability to use threads in cpp.