Filter BBS to specified time series period and number of samples

Modified from https://github.com/weecology/bbs-forecasting and https://github.com/weecology/MATSS-community-change

filter_bbs_ts(bbs_data, start_yr, end_yr, min_num_yrs)

Arguments

bbs_data	dataframe that contains BBS site_id and year columns
start_yr	num first year of time-series
end_yr	num last year of time-series
min_num_yrs	num minimum number of years of data between start_yr & end_yr

Value

dataframe with original data and associated environmental data