Rewrite #instrument
Rewrite #instrument

Only yields if block is given so #instrument can be called without one.

Clarifies conditional behavior when service is set.

astockwell/ruby-net-ldap,cloudvolumes/ruby-net-ldap,bkeepers/ruby-net-ldap,cloudvolumes/ruby-net-ldap,bkeepers/ruby-net-ldap,astockwell/ruby-net-ldap,javanthropus/ruby-net-ldap,javanthropus/ruby-net-ldap