modernizes spec_helper snippet
Update README.md

Updated instructions for changing directory in Windows to Sublime package folder.
Use modern require spec_helper syntax
Merge remote-tracking branch 'donaldevine/patch-1' into merge_recent_improvements
Remove deprecated target.should snippets
Update it {} and it 'des' do ... end snippets. Fabricate let snippet.
Revert the `let` helper back to its more generic earlier form
Update describe and context block snippets.

Conflicts:
	README.md (resolved with the shorter one for now)
Revert the `describe` tab trigger back to "des" to avoid a clash with the existing "desc"
Update expect() and expect { } snippets
Update README change in the previous commit that relates to the `let` change made and reverted in earlier commits
Shorten `expect` tab triggers and tweak some doc lines
Removed old 'should' syntax
Fix minor snippet description mistake
Small tweaks to the `describe` helpers
Simplify the `let` snippet and add a corresponding `let!`
Highlight `let!` and `subject!`
Add `pending` snippet
Minor tweak to the `let` and `let!` snippets
Adds snippet for 'subject'