Lack of support for Eurostat data flags.

[fpernice-google]

Eurostat uses the following flags to label their data:

b = break in time series
c = confidential
d = definition differs, see metadata. The relevant explanations must be provided in the annex of the ESMS (metadata)
e = estimated
f = forecast
n = not significant
p = provisional
r = revised
s = Eurostat estimate
u = low reliability
z = not applicable

Currently, these are being ignored (e.g. in #119). It would be great to have a property in StatVarObservations to surface these flags.