Add variable length messages to canlib send. change rust toolchain to use latest nightly instead of old nightly to fix compilation on newer embassy versions

[stackunderfl0w]

closes #44 Tested can0 040 [8] 48 65 6C 6C 6F 20 77 6F 'Hello wo' can0 040 [8] 72 6C 64 20 74 68 69 73 'rld this' can0 040 [8] 20 69 73 20 61 20 74 65 ' is a te' can0 040 [8] 73 74 20 6F 66 20 74 68 'st of th' can0 040 [8] 65 20 63 61 6E 62 75 73 'e canbus' can0 040 [8] 20 74 72 61 6E 73 6D 69 ' transmi' can0 040 [8] 73 73 69 6F 6E 20 73 79 'ssion sy' can0 040 [5] 73 74 65 6D 2E 'stem.'

[stackunderfl0w]

Code is aesthetically pleasing, tbh the compiler would probably generate something like your solution in lines 21,30(that's a good thing). I mean the compiler probably would hopefully optimize it to reuse the input data and just add the correct type tags