Write blueprint to YAML

[matt-dray]

Blueprints should be writable. They act as a record of the content that went into a given release, which is ideal for archival purposes. They could be saved as RDS and YAML.

Blueprints should be readable. A user should be able to edit a blueprint, probably programmticaly and perhaps even outside of an R session, and then read it into to R.

Saving a blueprint with e.g. yaml::write_yaml() means that data.frames are broken up into their constituent list elements (i.e. their columns). I think this is okay, we just need to make sure that this is recognised on read and that the data.frames are recombined. Consider this table from a user-built blueprint:

 $ Table_2 :List of 5
  ..$ sheet_type: chr "tables"
  ..$ title     : chr "The Title 2"
  ..$ subtitle  : chr "The subtitle 2"
  ..$ source    : chr "The source 2."
  ..$ tables    :'data.frame':	5 obs. of  5 variables:
  .. ..$ mpg : num [1:5] 18.1 14.3 24.4 22.8 19.2
  .. ..$ cyl : num [1:5] 6 8 4 4 6
  .. ..$ disp: num [1:5] 225 360 147 141 168
  .. ..$ hp  : num [1:5] 105 245 62 95 123
  .. ..$ drat: num [1:5] 2.76 3.21 3.69 3.92 3.92

Once we do yaml::write_yaml() on it and then yaml::read_yaml(), it comes in like:

 $ Table_2 :List of 5
  ..$ sheet_type: chr "tables"
  ..$ title     : chr "The Title 2"
  ..$ subtitle  : chr "The subtitle 2"
  ..$ source    : chr "The source 2."
  ..$ tables    :List of 5
  .. ..$ mpg : num [1:5] 18.1 14.3 24.4 22.8 19.2
  .. ..$ cyl : num [1:5] 6 8 4 4 6
  .. ..$ disp: num [1:5] 225 360 147 141 168
  .. ..$ hp  : num [1:5] 105 245 62 95 123
  .. ..$ drat: num [1:5] 2.76 3.21 3.69 3.92 3.92

Would just need to recognise that the elements under the tables element of sheets with sheet_type "tables" should be combined with data.frame() when ingested.