Merge pull request #886 from qtxie/float

FIX: Incorrect ROUND macros on ARM platform.
FEAT: added lexical support for negative floating point zero (-0.0).
Merge branch 'float' of github.com:red/red into float
FEAT: setting default exception flags for ARM FPU.
FIX: missing debug messages for verbose mode.
FEAT: wish #857 (`Do string!` is not implemented yet)

Red/System compilers directives (issue! values) are not allowed to be nested in code blocks.
FEAT: added string! TO float! action.