magit.el: improve doc-strings

This mostly just addresses issues that can easily be fixed (like using
imperative form, fixing punctuation and indention, fitting the first
sentence on the first line).
magit.el: improve doc-strings

This mostly just addresses issues that can easily be fixed (like using
imperative form, fixing punctuation and indention, fitting the first
sentence on the first line).
Merge branch 'maint'

Conflicts:
	magit.el
Merge branch 'master' into next