Improve shell syntax highlighting

[fregante]

This is the current highlighting for a .sh file, which is essentially zero. Can this be extended to at the very least highlight the command name and --flags? That'd go a long way

Example from fishell (no flag highlight but it underlines existing file paths):

---

• VSCode Version: Code 1.16.1 (27492b6, 2017-09-14T16:24:39.530Z)
• OS Version: Darwin x64 15.6.0
• Extensions:

Extension	Author (truncated)	Version
EditorConfig	Edi	0.10.1
beautify	Hoo	1.1.1
fish	Ted	0.0.4
vs-code-bitkompagniet-require	bit	0.7.0
vscode-svgviewer	css	1.4.3
vscode-eslint	dba	1.3.2
gitlens	eam	5.4.1
vscode-npm-script	eg2	0.2.1
code-runner	for	0.7.2
Untabify	ili	0.0.2
search-node-modules	jas	1.2.0
vscode-gutter-preview	kis	0.11.1
vscode-lebab	mrm	2.5.0
sublime-keybindings	ms-	2.9.1
typescript-javascript-grammar	ms-	0.0.24
debugger-for-ios-web	msj	0.1.2
node-modules-resolve	nau	1.0.2
peep	nwa	0.0.5
vscode-icons	rob	7.14.0
linter-xo	sam	2.1.3
trailing-spaces	sha	0.2.11
stylelint	shi	0.29.1
vscode-fileutils	sle	2.7.0
ayu	tea	0.8.0
shellcheck	tim	0.1.0
ghosttext	tok	1.0.2

[aeschli]

This issue was moved to textmate/shellscript.tmbundle#45