[#26] *: Move pkg content to root

Signed-off-by: Angira Kekteeva <kira@nspcc.ru>

policy/doc.go

@@ -0,0 +1,19 @@
+// Package policy provides facilities for creating policy from SQL-like language.
+//   ANTLRv4 grammar is provided in `parser/Query.g4` and `parser/QueryLexer.g4`.
+//
+// Current limitations:
+// 1. Filters must be defined before they are used.
+//    This requirement may be relaxed in future.
+// 2. Keywords are key-sensitive. This can be changed if necessary
+//    https://github.com/antlr/antlr4/blob/master/doc/case-insensitive-lexing.md .
+//
+// Example query:
+// REP 1 IN SPB
+// REP 2 IN Americas
+// CBF 4
+// SELECT 1 IN City FROM SPBSSD AS SPB
+// SELECT 2 IN SAME City FROM Americas AS Americas
+// FILTER SSD EQ true AS IsSSD
+// FILTER @IsSSD AND Country EQ "RU" AND City EQ "St.Petersburg" AS SPBSSD
+// FILTER 'Continent' EQ 'North America' OR Continent EQ 'South America' AS Americas
+package policy