man/cwebp.1, cosmetics: escape '-'s
man/cwebp.1, cosmetics: escape '-'s

+ consistently make references to switches bold
+ add the default for -pass

Change-Id: I84abd9c0c878f8804c0f5dec806ca654e00b6661

PKRoma/libwebp,ttyangf/libwebp,Aexyn/libwebp,webmproject/libwebp,PKRoma/libwebp,ttyangf/libwebp,Aexyn/libwebp,Aexyn/libwebp,webmproject/libwebp,redengineer/libwebp,PKRoma/libwebp,redengineer/libwebp,webmproject/libwebp,ttyangf/libwebp,PKRoma/libwebp,Aexyn/libwebp,webmproject/libwebp,ttyangf/libwebp,Aexyn/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,redengineer/libwebp,redengineer/libwebp,ttyangf/libwebp,redengineer/libwebp