Normalize whitespace in osproc.nim.
Introduce poEvalCommand, poUsePath, fix remaining quoting issues.

- poUsePath is now an alias for poUseShell.
- poEvalCommand should be used when shell evaluation is really needed.
It passes `command` directly to shell/winapi. Requires `args` parameter
to be empty.
Added docgen documentation
Fixes two minor typos.
Reformats text to fit width of 80 columns.
Adds docgen to list of documentation to build.
Adds some cross references to docgen manual.
Transforms docgen sample to be generated from source.
command syntax is allowed in expressions
updated grammar.txt
Merge branch 'osproc' into devel

Conflicts:
	lib/posix/posix.nim
	lib/pure/osproc.nim
fix the segfault in #827
parser support anon iterators
Merge branch 'devel' of https://github.com/Araq/Nimrod into devel
next steps for closure iterators
nest PreMain inside NimMain for easier consumption of static libraries developed in Nimrod

fixes many uses of $N instead of $n for new lines that don't affect #line directives
Adds AllChars constant to strutils.
fix the error "only proc headers can feature pragmas" when compiling in JS mode
closure iterators almost work
closure iterators work