Merge pull request #135 from bgamari/ioreg-docs

ioreg: Extend doc comment syntax
Export zinc::std for now

As demonstrated in #146 this is sometimes useful even outside of the
`zinc` crate.
ioreg/test: Add test for #140

Write-only registers shouldn't be read from.

Also remove parentheses from test names as this upsets the snake-case
lint.
Merge pull request #148 from bgamari/ioreg-test

ioreg/test: Add test for #140
k20: Add basic watchdog support.
app_blink_k20: Init watchdog on start.
k20/watchdog: Use helper instead of inline asm.
Merge pull request #150 from bgamari/master

Export zinc::std for now

Reviewed-by: farcaller
ioreg/getter: Clean up redundant lifetimes
ioreg/setter: Clean up redundant lifetimes
ioreg/accessors: Clean up redundant lifetimes
ioreg/union: Clean up redundant lifetimes
ioreg/register: Clean up redundant lifetimes
ioreg: Clean up redundant lifetimes
Merge pull request #153 from bgamari/ioreg-cleanup

ioreg: Clean up redundant lifetimes
Merge pull request #151 from dpc/master

Implement basics of #144 (watchdog)
ioreg::parser: Simplify field parsing

Also adds a bit of needed strictness.
Merge pull request #156 from bgamari/ioreg-docs

ioreg: More documentation fixes
hal::k20: Add DSPI registers
k20::spi: Add hal::SPI impl