fs 1.2.0

Breaking changes

• path_expand() and path_home() now use USERPROFILE or
  HOMEDRIVE/HOMEPATH as the user home directory on Windows. This differs
  from the definition used in path.expand() but is consistent with
  definitions from other programming environments such as python and rust. This
  is also more compatible with external tools such as git and ssh, both of
  which put user-level files in USERPROFILE by default. To mimic R's (and
  previous) behavior there are functions path_expand_r() and path_home_r().

• Handling missing values are more consistent. In general is_* functions
  always return FALSE for missing values, path_* functions always propagate
  NA values (NA inputs become NA outputs) and dir_* file_* and link_*
  functions error with NA inputs.

• fs functions now preserve tildes in their outputs. Previously paths were
  always returned with tildes expanded. Users can use path_expand() to expand
  tildes if desired.

Bugfixes

• Fix crash when a files user or group id did not exist in the respective
  database (#84, #58)
• Fix home expansion on systems without readline (#60).
• Fix propagation of NA values in path_norm() (#63).

Features

• file_chmod() is now vectorized over both of its arguments (#71).
• link_create() now fails silently if an identical link already exists (#77).
• path_package() function created as an analog to system.file() which
  always fails if the package or file does not exist (#75)