add buttons

src/mechanize/form/button.cr

@@ -0,0 +1,4 @@
+class MechanizeCr::FormContent::Button < MechanizeCr::FormContent::Field
+end
+require "./reset_button"
+require "./submit_button"

src/mechanize/form/reset_button.cr

@@ -0,0 +1,2 @@
+class MechanizeCr::FormContent::ResetButton < MechanizeCr::FormContent::Button
+end

src/mechanize/form/submit_button.cr

@@ -0,0 +1,2 @@
+class MechanizeCr::FormContent::SubmitButton < MechanizeCr::FormContent::Button
+end