Transform leveldb into a 'hybrid' package

This allows users to use leveldb databases in their own nim programs.

leveldb.nimble

@@ -5,6 +5,8 @@ author        = "Michał Zieliński"
 description   = "LevelDB wrapper for Nim"
 license       = "MIT"
 srcDir        = "src"
+installExt    = @["nim"]
+skipDirs      = @["tests"]
 binDir        = "bin"
 bin           = @["leveldb"]
 

src/leveldb.nim

@@ -1,4 +1,4 @@
-import options, strutils, leveldb/raw
+import options, strutils, leveldbpkg/raw
 
 type
   LevelDb* = ref object

tests/test.nim

@@ -1,5 +1,5 @@
 import unittest, options, sequtils
-import leveldb, leveldb/raw
+import leveldb, leveldbpkg/raw
 
 suite "leveldb":