add prepared_statements option to database

* use ?prepared_statements=true|false on connection string (default: true)
* make inmutable state in database
* make mutable state in connection
* change Connection#build to use the current prepared_statements flag to build prepared or unprepared statements.

spec/database_spec.cr

@@ -97,4 +97,36 @@ describe DB::Database do
       DummyDriver::DummyConnection.connections.size.should eq(2)
     end
   end
+
+  describe "prepared_statements connection option" do
+    it "defaults to true" do
+      with_dummy "dummy://localhost:1027" do |db|
+        db.prepared_statements?.should be_true
+      end
+    end
+
+    it "can be set to false" do
+      with_dummy "dummy://localhost:1027?prepared_statements=false" do |db|
+        db.prepared_statements?.should be_false
+      end
+    end
+
+    it "is copied to connections and can be changed (false)" do
+      with_dummy "dummy://localhost:1027?prepared_statements=false&initial_pool_size=1" do |db|
+        connection = DummyDriver::DummyConnection.connections.first
+        connection.prepared_statements?.should be_false
+        connection.prepared_statements = true
+        connection.prepared_statements?.should be_true
+      end
+    end
+
+    it "is copied to connections and can be changed (true)" do
+      with_dummy "dummy://localhost:1027?prepared_statements=true&initial_pool_size=1" do |db|
+        connection = DummyDriver::DummyConnection.connections.first
+        connection.prepared_statements?.should be_true
+        connection.prepared_statements = false
+        connection.prepared_statements?.should be_false
+      end
+    end
+  end
 end

spec/db_spec.cr

@@ -97,4 +97,15 @@ describe DB do
       DB.open "foobar://baz"
     end
   end
+
+  it "should parse boolean query string params" do
+    DB.fetch_bool(HTTP::Params.parse("foo=true"), "foo", false).should be_true
+    DB.fetch_bool(HTTP::Params.parse("foo=True"), "foo", false).should be_true
+
+    DB.fetch_bool(HTTP::Params.parse("foo=false"), "foo", true).should be_false
+    DB.fetch_bool(HTTP::Params.parse("foo=False"), "foo", true).should be_false
+
+    DB.fetch_bool(HTTP::Params.parse("bar=true"), "foo", false).should be_false
+    DB.fetch_bool(HTTP::Params.parse("bar=true"), "foo", true).should be_true
+  end
 end

spec/statement_spec.cr

@@ -17,6 +17,24 @@ describe DB::Statement do
     end
   end
 
+  describe "prepared_statements flag" do
+    it "should build prepared statements if true" do
+      with_dummy_connection do |cnn|
+        cnn.prepared_statements = true
+        stmt = cnn.query("the query").statement
+        stmt.as(DummyDriver::DummyStatement).prepared?.should be_true
+      end
+    end
+
+    it "should build unprepared statements if false" do
+      with_dummy_connection do |cnn|
+        cnn.prepared_statements = false
+        stmt = cnn.query("the query").statement
+        stmt.as(DummyDriver::DummyStatement).prepared?.should be_false
+      end
+    end
+  end
+
   it "should initialize positional params in query" do
     with_dummy_connection do |cnn|
       stmt = cnn.prepared("the query").as(DummyDriver::DummyStatement)