Update README.md
enusure checking only one times (when function is fresh)

renamed previously designed (not implemented) first_start mode to fresh_start. It is implemented
now - flag about checking is stored in session persistent hash table. Passive mode supports a non
fatal errors behave now - plpgsql_checks raises warnings instead errors.
return back context field,

remove bogus lineno when statement is unknown
Delete plpgsql_check--0.7.sql
minor fixes in README