Improved documentation, and other small changes. py core: - add builtin round function - gc.enable/disable still allows manual GC (as per CPython) - fix builtin callable for user-defined types - fix bug for right shift of small int by large amount unix port: - add "fast" version - improve uctypes, including sizeof function stmhal port: - support for extended CAN frames - USB_VCP works with select - experimental support for RTS/CTS in UART - make UART bits count number of data bits, not incl parity - pyb.freq now allows 8MHz and 16MHz docs: - revamp and merge all inline docs into Sphinx framework - add a few more tutorials