Fixes Issue 9092 - GC.extend allocates less then it reports

Not an actual issue, but required more documentation to be clear: Added a note about how extend and arrays interact to avoid confusion.

Also adds an example section, for both ways of using extend.
Documenting capacity/reserve/assumeSafeAppend
tweak extend documentation
typos
documentation tweaks and fixes
Documented unittests
Rework documentation
Merge pull request #382 from monarchdodra/9092

Fixes Issue 9092 - GC.extend allocates less then it reports
no default lib when making druntime.so
simplify rt.sections_osx.getSection

- only check for target specific mach header
Merge pull request #462 from WalterBright/nodefaultlib

no default lib when making druntime.so
Merge pull request #463 from dawgfoto/getSectionOSX

simplify rt.sections_osx.getSection
Add Windows error code ERROR_INSUFFICIENT_BUFFER.
Merge pull request #466 from jacob-carlborg/windows_error_code

Add Windows error code ERROR_INSUFFICIENT_BUFFER.