Added new units to Units.pm

[duffee]

This PR adds the Becquerel, the measure of radioactivity, and extends the second, metre, electron-volt, Coulomb, ampere and tesla to mostly smaller prefixes for electric and magnetic units. These are used in the areas of electromagnetism and nuclear physics with a couple for problems on optics and large power projects. Tests have been added for the new units in t/units/. It also corrects the spelling of mili to milli (double L).

When writing the test for adding new units with an optional hashref, the tests failed using syntax that I use in working problems. I've wrapped them in exception handling blocks and marked them with TODOs so that they pass, but are available for examination.

One point that might warrant discussion is the milliampere. I've added it as mamp which is consistent, but unappealing as it's not obvious what it is. I've also added mA which is in line with SI convention.

Units added:
microsecond, nanosecond
picometre, femtometre
tera electron-volt
Megawatt, milliwatt
milliCoulomb, microCoulomb, nanoCoulomb
milli-ampere
milli-tesla
Becquerel

[pstaabp]

Just to be clear, this doesn't changes the ampere unit to 'A'. correct?

I think you mentioned in #743 that this PR could be updated to include it.

[duffee]

Correct - this PR doesn't change the ampere unit to A. I think that an alternative or alias for Angstrom needs to be added first, so that people have a chance to migrate to the new unit.

I have added the milliamp as both mamp and mA in anticipation that the ampere will eventually change from amp to A.

[drgrice1]

@pstaabp: I thought you said that all of these tests were working. I guess I should have tried it myself. They aren't working.