NuGet: support building symbol+source packages without project file

NuGet supports building symbol/source packages automatically when
specifying the project file. However, it is also possible to build
such packages manually without a project file but instead a nuspec file,
where the symbols and sources are specified explicitly.

The default behavior is unchanged: symbol packages are built if and only
if a project file is provided (in this case we generate, as before, first
both packages with the project file, then overwrite the normal package
using the generated nuspec). If symbol packages should be built with the
nuspec file, then specify p.Symbols = NugetSymbols.Nuspec.
passing optional script arguments into deployment script
Merge pull request #450 from cdrnet/nuget-symbolsource

NuGet: support building symbol+source packages without project file
fix Fake.Deploy.Web compilation
Merge pull request #453 from vasily-kirichenko/deploy-script-arguments

Pass optional script arguments into deployment script
Bump version to 2.17.9
New (backwards compat) CLI for FAKE.
* New CLI for FAKE that uses UnionArgParser.
* If new CLI cannot parse, use old CLI for backwards compat.
* Strongly typed and easy to read and modify.
* Less brittle in face of changes needed for #438 etc.
* Generates documentation.
* Supports combination with app.config settings.
* Support long and short switches (e.g. --version or -v).
* Support multi-values (e.g. --envVar key value --envVar key value).
* Make env flag switches explicit (i.e. --envFlag nameWhoseValWillBeTrue).
* Print old and new help.
Merge remote-tracking branch 'upstream/master' into new-cli

Conflicts:
	src/app/FakeLib/FSIHelper.fs
Fix debug command line arguments (had left some local test ones in previous commit).
add RoundhouseHelper
Add FsCheck to users
Merge pull request #458 from kurtschelfthout/patch-2

Add FsCheck to users
* Make script and target positional arguments on the new CLI.
* Update usage documentation strings and usage print function.
* Add basic tests for CLI positional argument parsing.
Merge remote-tracking branch 'upstream/master' into new-cli
Added FundApps to users list
Removed HTTPS
Merge pull request #460 from jamescrowley/patch-1

Added FundApps to list of people using F# make
Merge pull request #456 from ChrisMissal/roundhouse

Add RoundhouseHelper
Merge remote-tracking branch 'upstream/master' into new-cli
Remove usage of F# 3.1 named DU values as not supported on the Travis CI build server.