[twgit] Init feature 'feature-136'.
replace os detection by function testing
fix os compatibility
fix sed
fix for zsh
replace result testing by error code testing
up CHANGELOG + README for #136
[twgit] Init hotfix 'hotfix-1.15.1'.
Merge branch 'feature-137' into hotfix-1.15.1

Conflicts:
	CHANGELOG.md
	README.md
Merge branch 'hotfix-1.15.1' into stable