fix a bug in `rake spec' which it would raise an ArgumentError when use "it" without block

A following spec will raise an ArgumentError.

	describe "Application 'test'" do
	  it "has one window"
	end

`instance_eval' will pass a receiver object into block.
When use a block which created by lambda, it should accept a receiver object as block parameter.

	b = lambda { self.upcase }
	"test".instance_eval(&b) #=> wrong number of arguments (1 for 0) (ArgumentError)
fix a tap format in `rake spec' to output the each test numbers instead of the total number

## before
$ rake spec output=tap
ok 34  - works with Assets
ok 34  - works with hash
…
ok 34  - should work
1..34
# 34 tests, 61 assertions, 0 failures, 0 errors

## after
$ rake spec output=tap
ok 1   - works with Assets
ok 2   - works with hash
…
ok 34  - should work
1..34
# 34 tests, 61 assertions, 0 failures, 0 errors
add a message of `describe' to description of tap's output

## before
not ok 1 - has one window: FAILED

## after
not ok 1 - Application 'test' has one window: FAILED
remove a `#' if it is included in first character in tap's description because its description will handled as comment in tap format
add app/pixate_code.rb into the default .gitignore file because it contains the Pixate license key