Tokenizer 1.18.4

Fixes and improvements

• Fix segmentation fault on cli/tokenize exit
• Ignore empty tokens during detokenization
• When writing to a file, avoid flushing the output stream on each line
• Update cli/CMakeLists.txt to mark Boost.ProgramOptions as required

(This is the first release to be created on GitHub. See the release note of previous tags in CHANGELOG.md.)