REFACTOR: reverse conditional

negative conditions are slightly harder to comprehend
Make property/field access case-insenstive.
`-ne` comparison, for int only.
Stop making Irony's Unnamed terms transient.

Better if we can stay a little closer to the official Irony source.

Also, notice that this code was indented but did not have braces. Oops/uggh.
IRONY: Make Unnamed nodes more obvious.
REFACTOR: Introduce `argument_list_opt` to avoid an unnamed grammar term.
Update README.md

Only show Travis build status icon for `master` branch.
Remove 1/2 of a Shift/Reduce error

Grammar Explorer reported 2 different reduces this could be, and now I have eliminated one of them.
Eliminate a shift/reduce error around member access.

I admit I am at the edge of my understanding, so I am not certain this is
the right change. But I like seeing the count of errors drop.
Eliminate a shift/reduce error around `for` statements.

I admit I am at the edge of my understanding, so I am not certain this is
the right change.

One consenquence of this change is that the parser will allow:

    for (;;;) { }     # Should be illegal - 2 semicolons max

and of course, pipelines between those semicolons:

    for ( $x = 0 ; $x -lt 10 ; $x++ ; echo $x ) { }    # should be illegal

We'll check for that in post-processing, or fix the grammar.
REFACTOR: Rename ParserTests assembly to Pash.System.Management.Tests.

I'm aiming for a 1:1 mapping between code assemblies and test assemblies.
Rename a little more.
REFACTOR: Move `ParserTests` to `Pash.ParserIntrinsics.Tests`

So directory & namespace that matches code under test
TEST: Make it easier to debug unit tests.

With this change, I was able to attach to the nunit.exe process to debug
my tests.
TEST: `Set-Location ; Get-Location`
replace many many usages of 'string path' with 'Path path' in prep for a cleanup on path usages
removed some use of Substring and pushed pathing logic down into the Path object
added a number of tests around the Path object
moved path combination into the path object
tweaked the getDrive code to support 'get-childitem /'