Bugfixes and bash completion

• CLI: Add bash completion for the minify command
• CLI: improved error messages
• CLI bugfix: don't open all files at once when concatenating, which usually panics when >10000 files are open
• CLI bugfix: don't minify modified files twice when watching them
• Bugfix: prevent panic on long decimals with negative exponent, where rewriting would previously cause longer numbers
• HTML: accept alternative syntax for MS conditional comments
• HTML bugfix: draggable is not a boolean
• HTML bugfix: do not assume mediatype in <meta content="x">
• CSS: add option for CSS2 numbers without exponents
• CSS: trim space in url()
• CSS: minify box-shadow, background and @import better
• CSS bugfix: prevent panic for functions with no arguments or end parenthesis
• CSS bugfix: keep dimensions for zeros in flex property
• CSS bugfix: keep other values for outline and border when width is zero
• CSS bugfix: font normal now handled
• CSS bugfix: add quotes to unquotes url() when we can remove the url function
• CSS bugfix: only omit number dimensions for and
• JS bugfix: ASI behaviour for template literals
• JS bugfix: replace comment as space when comment is removed
• JS bugfix: divide by regular expression
• SVG: don't remove empty groups anymore, as CSS or JS might rely on them
• SVG bugfix: prevent panic on invalid pathdata for arcs