Write-Message: the common messaging function. Closes #8.
Close-SvnBranch: add Closed configuration value. Closes #9.
Get-SvnBranch: remove the trailing slash from the output. Closes #21.
Merge-SvnBranch: determine branch source before switching (this solves the problems with a "current branch" option). Closes #24.
README: update formatting.