Fix filter mode
Fix interned string hashing, we need to hash content
Tweak Value constructor, no need for the const ref one
Fix unneeded WordDB copy in complete_word
Refactor word_db, use an unordered map
mark InternedString move constructor noexcept
Add noexcept spec to move constructor and move assign
Style fixes
Add some asserts in StringRegistry methods
Fix invalid memory access when applying modifications on an empty buffer

That can happen when undoing/redoing accross a buffer reload
boundary.
Optimize the test run script