Prepare version 0.19-6

Add tests

[.pl] Compute profit/loss with %*%

Fix space

[unit_prices] Add arguments 'round.price' and 'round.units'

Update NEWS

Refactor 'unit_prices'

unit_prices: refactor function and add more checks; in
particular, check if 'NAV' is sorted by time

.unit_prices: remove unexported function, which has been
deprecated since 2020; see ChangeLog 2020-11-22

Update documentation.

Update NEWS

Fix printing of total returns for 'x' without 't'

Rename argument 'initial.shares' to 'initial.units'

Add a warning when there are missing values

Add DOI

Prepare version 0.19-5

Add link to 'zoo' package

Add tests

Split multivariate zoo-series into a list of NAVseries

Update docs

Add notes

Update http ==> https

Update NEWS