v0.9.1

• fixed SVG inlining not preserving original image class attributes
• fixed ValueError when reading some SVG files
• fixed navbar option allowing duplicates
• fixed custom navbar items always being transformed to lowercase
• fixed navbar generating links to empty pages
• added concepts to the default set of links in navbar
• added navbar values all and default
• reduced I/O churn during HTML post-processing
• removed command-line option dry