separate function for "land use" and population data.

[rafapereirabr]

The reason for this is beacause they como from different years.

• Land use data is annual data from 2017 onwards.
• Current population data is from the 2010 census. We will eventually add population data from the next census (2021? 2022?)

[rafapereirabr]

The population data changes less often, so I would consider include the population data sets as separate data files published within the R package.

[rafapereirabr]

• [x] save population data
• [x] update metadata
• [x] create read_population() fun
• [x] adapt read_access() and read_landuse() functions