chore: Prep for CRAN release

* Bump version number
* Update test environments used by `cran-comments.rst`
* Tweak permanently moved URL addresses to suppress CRAN NOTE

chore: Tweak URLs [skip ci]

fix: Fixes hledger date import for newest versions of hledger

* Fixes hledger date import for newest versions of hledger
  because of a non-reverse-compatible change in date format:
  simonmichael/hledger#1157
* Thanks Chris Lloyd (@chrislloyd) for bug report and patch (#19).

Closes #19

chore: CRAN release 2.0.6

chore: CRAN release

chore: Tweak .gitignore [skip ci]

chore: CRAN release 2.0.0