updated Duration.milliseconds() to return an integer, and added floating point math

[martin770]

I updated duration.milliseconds() to truncate partial milliseconds and return an integer to fix issue #4649 while allowing duration.asMilliseconds() to still return a non-integer number.

As I was adding test cases for it, I noticed that some of the calculations were incorrect due to javascript floating point math problems. See: #2978 and #1867

I added a function (fpMath) to correctly perform floating point calculations, and added test cases around that to make sure everything is behaving as expected. I did not have to modify any existing test cases, so this should not negatively affect any existing functionality.

I only modified files in /src/ and all the tests are passing, but I wasn't sure if I need to also make the changes to /moment.js also or if that file gets built from src somehow.

[jsf-clabot]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

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[martin770]

You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.

I signed the CLA, but it says my e-mail address is not linked to my github account. I checked my profile, and it's there...

[marwahaha]

@martin770 - your git commits aren't with the same email address, please update them