Update version number and update documentation

* Improve portability of `hostname` (#23)
* Fix incompatibilities between Cygwin and Git for Windows (#26)
* Allow Git program to be configured via yadm.git-program (#30)
* Support alt-links for encrypted files (#34)
* Exit with the same return value as Git (#35)
* Support spaces in alt-link paths (#36)
* Ignore empty lines in .yadm/encrypt (#40)
* Fix typos (#41)