Don't use silent when raising User events

[PhilRunninger]

Description of Changes

Closes #1163

The silent prefix is there to prevent the display of the No matching autocommands warning message. Leaving it in, though, prevents the display of debugging statements in functions that handle the event. As suggested by @tpope, my solution is to remove the silent and wrap the doautocmd statement in an if exists('#...') clause.

---

New Version Info

Author's Instructions

• Derive a new MAJOR.MINOR.PATCH version number. Increment the:
  • MAJOR version when you make incompatible API changes
  • MINOR version when you add functionality in a backwards-compatible manner
  • PATCH version when you make backwards-compatible bug fixes
• Update CHANGELOG.md, following the established pattern.

Collaborator's Instructions

• Review CHANGELOG.md, suggesting a different version number if necessary.
• After merging, tag the commit using these (Mac-compatible) bash commands:

  git checkout master
  git pull
  sed -n "$(grep -n -m2 '####' CHANGELOG.md | cut -f1 -d: | sed 'N;s/\n/,/')p" CHANGELOG.md | sed '$d'
  git tag -a $(read -p "Tag Name: " tag;echo $tag) -m"$(git show --quiet --pretty=%s)";git push origin --tags