v0.18

• Add support for loading multiple TMC location databases by specifying --loctable more than once.
• Sample rate can also be specified as -r 171k instead of -r 171000.
• Fix a crash if the input audio file couldn't be loaded.
• Print usage help instead of error message when stdin is empty.
• Speed up loading of TMC location database.
• Improve block sync detection by ignoring spurious sync pulses.
• Fine-tune filter bandwidths for better sensitivity, based on test runs.
• At EOF, process the last partially received group.
• Remove character codetables G1 and G2 since they don't appear in the latest RDS standard any more.
• Clean up code to ensure maintainability. Redsea now requires a compiler that supports C++14.