inconsistency: configuration dictionary and environment variables

[jkwashbourne]

there is an inconsistency between some configuration dictionary keys and corresponding environment variables. Examples below.

config	variable	notes
mpi	DEVITO_MPI	consistent
language	DEVITO_LANGUAGE	consistent
platform	DEVITO_PLATFORM	consistent
compiler	DEVITO_ARCH	inconsistent
log-level	DEVITO_LOGGING	inconsistent

[georgebisbas]

@FabioLuporini @mloubout is there any plan to change this?