Certain units do not work

[bradleymarques]

The following units raise AttributeErrors when using them:

1. Distance - british_ft
2. Distance - british_yd
3. Distance - german_m
4. Distance - gold_coast_ft
5. Distance - indian_yd
6. Distance - nm_uk
7. Distance - sears_yd
8. Distance - survey_ft

Example:

from measurement.measures.geometry import Distance

distance = Distance(m=1)
distance.nm_uk

# AttributeError: Distance object has no attribute 'nm_uk'