Log Message:
(math/R-units) Updated 0.6.5 to 0.7.1

# version 0.7-1

* allow longer units grouping; #270 addressing #269 @bart1

* fix regression in `set_units` method for `mixed_units` to ensure that
  ordering is preserved; #272 addressing #271

# version 0.7-0

* add `load_units_xml` to enable database reloading as well as loading
  user-provided unit systems; #254 addressing #243, #244

* add `install_unit` and `remove_unit` for adding/removing custom user-defined
  symbols or names, with optional mapping to existing units;
  `install_symbolic_unit`, `remove_symbolic_unit`, `install_conversion_constant`,
  `install_conversion_offset` are deprecated; #261 addressing #89

* add `keep_units`, a helper to apply functions that do not preserve units;
  #255 addressing #252

* fix `as_units("")`, which is now equivalent to `unitless`; #199

* fix plot axes for `plot.formula` and `plot.data.frame`; #213

* fix arithmetic for powers above 1 and below -1; #264

* improve arithmetic of logarithms; #249

* export `ud_are_convertible`; #263 addressing #258 @cregouby

* remove deprecations: `as.units`, `as_cf`, `make_unit`, `parse_unit`; #259

* remove deprecated pre-computed `ud_units` database; #259

# version 0.6-7

* port `isFALSE` to fix regression in old R versions; #230 addressing #229

* fix replacement operation for `units` objects; #233 addressing #232

* fix compatibility with dplyr 1.0; #247 addressing #239

# version 0.6-6

* prettier `str` print for units and mixed units; #228 addressing #227

* add compatibility with upcoming tibble v3.0.0; #225