The core folder is now a symlink to a versioned folder

This will allow to work on different versions of core from
different branches without having to repeat the download
Merge branch 'master' into ez-core-symlink

* master:
  delete build/bin, otherwise the symlink will fail
  There are a few implicit casts stopping master from successfully testing/building in Realm.xcodeproj
  Upgrade to use core library version 0.80.3
  changelog
  Using the Realm’s schema when validating relationship queries.
  Core does only support link queries in the for X.Y.
  add transaction block helper
  Safer string conversion
  ANY does also work
  A little style
  Cleaning up unit tests and adding more explaination to the changelog
  Support for querying objects' RLMArray properties
  Updating changelog
  Adding basic support link queries
  Version bump
  Move build.log into the build folder
  No need to remove the bin folder now
  Move the bin symlink into the build folder
  make property initializer private, update swift
  add JP's dynamic tests, fix for setting usig object subscripting on standalone objects
Merge pull request #632 from realm/ez-core-symlink

The core folder is now a symlink to a versioned folder