pxmake 0.10.0

New features

• The function px() creates a px object. This is a major change to the way
  package works. pxmake and metamake are soft deprecated. Use px() and pxsave() instead. (#197)
• To modify the px object, a number of modifying functions have been added:
  charset(), creation_date(), decimals(), matrix(), stub(), heading(),
  timeval(), add_totals() and figures(). Many more need to be added in the
  future, to cover all px keywords.

Breaking changes

• The 'rds' version of the px file is completly gone. Neither pxmake() nor
  metamake() can create them. pxmake() and metamake() can convert between Excel
  and px files, and they return a px object invisibly. pxmake() and metamake()
  will be deprecated in the future.
• make_template() will be deprecated in the future - px() automatically
  creates a metadata template if none is provided.
• micromake() now takes a px object as input.
• add_totals() now takes a px object as input.

Bug fixes and minor improvements

• README.md has been rewritten, and includes a list of all keywords with
  modifying functions. All vignettes have been removed.
• README.md is now created from README.Rmd using knitr::knit().