Improve describe_categorical_1d() performance
Improve describe_categorical_1d() performance

A few changes have been done:

- Create variable `count_column_name`, rather than running `"count({c})".format(c=column)` again and again
- remove the usage of `f-string`. It's only supported from Python 3.6. This package is not using any special feature of Python 3.6+, so no point at all to break support to Python 2.7 and Python 3.4/3.5
- Much more efficient way to calculate `others_count` and `others_distinct_count`. According to my local simple testing, it reduces the time needed by more than half (~60 seconds -> ~25 seconds).
julioasotodv/spark-df-profiling,julioasotodv/spark-df-profiling