Save and Flush hooks introduced

The following hooks were introduced in the update:

• pre and post hook for save
• pre and post hook for flush

Note: currently the hooks are not async, next update will include async hooks

Bug fix: save fixes

Bug fix for document not getting saved

Support for constructor classes

This release adds the following support:

• Localstorm now supports constructor classes, i.e Array, String.
• Expanded schema definition to support required validation for mandatory fields
• skipValidation support to bypass validations