terminology issue

[mark-riscv]

in this section. a new phrase "may not be supported" is introduced. shouldn't it be unsupported optional?

==== RVI20U32 Mandatory Base

RV32I is the mandatory base ISA for RVI20U32, and is little-endian.

The ecall instruction causes a requested trap to the execution
environment.

Misaligned loads and stores might not be supported.

The fence.tso instruction is mandatory.

[kasanovic]

"may not" not present in current text.

It is probably time to add names for the different types of misaligned support.