Introduce query language (resembling reprepro syntax).

query/query.go

@@ -0,0 +1,17 @@
+// Package query implements query language for
+package query
+
+/*
+
+  Query language resembling Debian dependencies and reprepro
+  queries: http://mirrorer.alioth.debian.org/reprepro.1.html
+
+  Query := A | A '|' Query
+  A := B | B ',' A
+  B := C | '!' B
+  C := '(' Query ')' | D
+  D := <field> <condition>
+  field := <package-name> | <field> | $special_field
+  condition := '(' <operator> value ')' |
+  operator := | << | < | <= | > | >> | >= | = | % | ~
+*/