*tested and fixed compliance with ports of sarcduino objects so that their channel numbers correspond with those on arduino uno board

improved installer to avoid install of Gem libraries when doing incremental install (should significantly shorten incremental installs)

*cannot create two structs on the same canvas (otherwise how would you know which one you are talking to)?
*fixed regression where arbitrary font sizes were not honored by the drawsymbols and drawnumbers
*other minor clean-ups
*adjusted help file to reflect the new approach to font sizes

cleaned-up gpio external dependencies and supporting build script. made disis_gpio external into a comprehensive object for all things gpio, including pwm (both hardware and software) with sarcduino-like formatting and verbose output. The external requires sudo due to required access to /dev/mem and /sys/class/gpio

*added new externals for raspberry pi (disis_gpio for digital I/O and disis_spi for analog I/O using mcp3008 A/D converter). Provided preliminary help files. PWM on gpio needs to be tested further. So does the build script. TODO: add this to the installer, including 4755 chown_gpio script.