Update getrandom to 0.2

[josephlr]

Per discussion in #889, we are keeping getrandom optional. Users can now specify custom RNG handlers for getrandom on any target. However, not all users will want OsRng, so getrandom needs to be optional.

Signed-off-by: Joe Richey [email protected]

[dhardy]

Thanks @josephlr.

The codes CUSTOM_START and INTERNAL_START can now be re-exported from getrandom I believe. But, see #984: we should probably document exactly what these values are and assert that they will never change.

[vks]

@dhardy I don't think we can re-export them as long as getrandom is an optional dependency. Instead, I documented the error codes as being identical to the ones in getrandom and added a test to make sure.

[josephlr]

@dhardy I don't think we can re-export them as long as getrandom is an optional dependency. Instead, I documented the error codes as being identical to the ones in getrandom and added a test to make sure.

Thanks! I also updated the comments to link to the getrandom documentation.