maintainer+doc: remove trailing whitespace
doc: remove @overridable

In no case should behavior depend on undefining and subsequently redefining
a configuration macro.
doc: rename @platformdefault to @platformvalue

The point of this is that the value must be obtained from
<bsp430/platform.h>.  That value may be @defaulted is a separate issue.
doc: validate @defaulted with @platformvalue

Most platform-specific values cannot be overridden through a prior
definition, but some can.
doc: eliminate @nodefault, add @dependentvalue

For some of these there is now a default, though there may not have been at
the time the documentation was reviewed.  In the remainder the default
depends on other configuration values and can't be trivially described.
doc: eliminate @delegated

This annotation serves no useful purpose.
coding: describe use of documentation annotations
doc: review and refine coding standards related to configuration

This includes where configuration options should be specified, how they are
used, and the requirements on include file ordering to ensure consistency
across a build.
style: enclose all conditional flag expressions in parentheses

The C style guidelines require full parenthesization of complex
expressions, and enclosure of single-statement blocks in braces.  That
the C preprocessor does not require parentheses around complex
expressions is irrelevant.  Make "#if X - 0" be "#if (X - 0)" because
it's just cleaner and more consistent.
doc: distinguish @platformvalue from @platformdep
cc2520: add missed VREGn pin on CC2520EMK
doc: replace annotation names with links