Use explicitly sized types from stdint

Replace bare int types with stdint types. This was done with:

    grep -rwl 'int' src/ | xargs sed -i 's/\<int\>/int16_t/g'
    grep -rwl 'unsigned long' src/ | xargs sed -i 's/\<unsigned long\>/uint32_t/g'
    grep -rwl 'unsigned char' src/ | xargs sed -i 's/\<unsigned char\>/uint8_t/g'

Then reverted for *main(), putchar(), and getchar().

The Arduino declarations for parallel_main() were also corrected to
match their definitions.

SDCC does *not* generate the same code in all instances, due to `int`
being treated different than `short int`.

Signed-off-by: Tim Crawford <tcrawford@system76.com>

src/board/system76/common/stdio.c

@@ -17,7 +17,7 @@
 #endif // PARALLEL_DEBUG
 
 int putchar(int c) {
-    unsigned char byte = (unsigned char)c;
+    uint8_t byte = (uint8_t)c;
 
     smfi_debug(byte);