Other archs use `_sheap` and `_eheap` to mark the start and end of
the heap.
fe310 uses `_heap_start` and `_heap_end`, so platform independent
code that wants to make use of this will needlessly fail.
For compatibility with common code, name them the same on fe310.
Added HiFive1 to BOARD_INSUFFICIENT_MEMORY list for examples and tests that are too big to fit
build: fixed missing syscall and cpuid failures
Added missing syscall stubs for nanostubs and fixed compile error with cpuid periph
build: fixed whitespace error
build: add hifive1 to more BOARD_INSUFFICIENT_MEMORY
doc: fixed doxygen warnings
Addressed Doxygen warnings in source file comments
doc: more doxygen fixes
doc: even more doxygen fixes
doc: more changes
build: fix pedantic and rdci_simple build failures
make: exclude lua
