Duration methods (total_days(), in_days()) return incorrect values and/or do not match docs

[hamblin]

• I am on the latest Pendulum version.

• I have searched the issues of this repo and believe that this is not a duplicate.

• OS version and name: MacOS 10.14 (running Python 3.7.2)

• Pendulum version: 2.1.0

Issue

The duration methods duration.total_days() and duration.in_days() do not match expected results, and/or do not match the docs. Since the docs seem to show an inconsistent / incorrect result (specifically for duration.in_days()), it isn't clear what the real expected behavior is.

I was quite confused about the logic and differences between the conversion of years/months into days for a duration (still am), so I just re-created the example used in the docs in order to test my thinking. And when doing that, I got different results to what is shown in docs.

My results below, using exact example from Pendulum docs duration section:

# I copied example from pendulum docs
>>> it = pendulum.duration(
...     years=2, months=3,
...     days=1177, seconds=7284, microseconds=1234
... ) 

>>> it.days
1997   
# seems OK... 2 * 365 days/year + 3 * 30days/month + 1177 days = 1997

>>> it.total_days()
1177.0843055698379   
# this matches result shown in docs (1177.084...)
# but result seems counter-intuitive based on name of method
# I would expect 'total_days' to be 1997.084... including days from years and months

>>> it.in_days()
1177  
# this DOES NOT match result shown in docs (docs show 1997 for it.in_days())
# but does match description of this method being truncated integer of total_days()

Based on description of duration.in_days() method in the docs, I would expect duration.total_days() and duration.in_days() to return same result, only with in_days() as a truncated integer as described. That's what I actually got, but doesn't match docs.

But larger issue seems to be that both .total_days() and .in_days() return incorrect (or at least un-intuitive) results -- I would expect them to both return 1997... in this case, including the days from years and months. (not 1177)

Seems like there is either:
A) Incorrect example in the docs (specifically where it shows return of 1997 for .in_days() method)
B) Bug in duration.in_days() and/or duration.total_days() method, especially when including years/months in duration
C) Both A and B
D)or I'm totally missing something...

This may be related to #387 but I'm creating this as separate bug because it seems there is at least a docs issue here, and because 387 relates to total_seconds() and maybe there are drop-in compatibility constraints with built-in total_seconds() method for that one?

Thanks to the creator & contributors!