Updated inline asm for UART send/receive#1
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…nd reduced register clobber list.
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I have fixed some minor mistakes with regards to the inline assembly for the UART transmit and receive functions.
The constraints for the input delay counts (txdelay, rxdelay, rxdelay2) were over-restrictive. The ldi instruction can accept an 8 bit value, but the previous constraints limited it to a 6 bit value.
The UART transmit inline assembly was using some registers it probably shouldn't (pointer register y r29:r28). I also suffixed the labels with a unique number for each asm instance; this is to avoid problems with duplicate assembly labels if the compiler inlines functions that call the UART transmit function (I had this happen to me when using the -Os compiler flag).
The register clobber list for the UART receive included unnecessary registers.
AVR-GCC inline asm reference: http://www.nongnu.org/avr-libc/user-manual/inline_asm.html