Fix usage string ("[-v]" not "[v]").
Don't use assert unless HEATSHRINK_DEBUGGING_LOGS is set.
Add braces around statements hanging off `if`s that may compile out to no-ops.
Update greatest.h to 0.9.3, increase warnings & make warning-free.
Add warnings from -Wextra
Fix some (potentially) unused variable and numeric type warnings
Add travis-ci file.