add template functions

[ThisGuyCodes]

I find myself needing some more basic math when making more dynamic/flexible templates:

• resize columns based on max width of shown values
  • "assignee" has max width of 10, but this list only has 4-character names
• dynamically set summary column width based on width of other columns
  • makes templates easier to change
  • works well with dynamic resizing

I'm iffy on adding division, but seemed prudent given the others I added.

[ThisGuyCodes]

I cannot reason about which test failed (I just see "1 of 94"), but it looks to me like it's an integration test.

I don't think it has anything to do with my changes, but if anyone knows how I can fix it let me know.

[coryb]

Not sure what is up with the test failure, might be random, it has been a while since I ran them.

I was wondering if you have looked at https://github.com/Masterminds/sprig I think all of the functions you added could be imported from sprig and then we would get extra goodies for "free".

-Cory

[sstarcher]

Sprig would be a nice addition

[coryb]

I ended up adding sprig in #283 so all the template functions you wanted should be available now with the exception of prod is added as mul. More docs here:
http://masterminds.github.io/sprig/

I am going to close this PR out now.