compiler: make compiler an ordinary vlib/compiler module

* Move compiler/ under vlib/compiler/ .

* Add a minimal compiler/main.v driver program.

* Cleanup compiler/main.v .

* Make most compiler tests pass again.

* Apply the fix by @joe-conigliaro , so that the rest of the compiler tests are fixed too.

* Thanks to @avitkauskas, now the vlib/vcompiler/tests/str_gen_test.v test does not need to be special cased anymore.

* Reapply @joe-conigliaro fix for vgen.

vlib/compiler/tests/struct_test.v

@@ -0,0 +1,120 @@
+struct A{
+mut:
+	val int
+	nums []int
+}
+
+struct B{
+mut:
+	a A
+}
+
+struct C {
+mut:
+	b B
+	nums []int
+	aarr []A
+	num int
+}
+
+struct User {
+	name string
+	age int
+}
+
+struct Foo {
+	@type string
+}
+
+//We need to make sure that this compiles with all the reserved names.
+struct ReservedKeywords {
+	delete   int
+	exit     int
+	unix     int
+	error    int
+	malloc   int
+	calloc   int
+	free     int
+	panic    int
+	auto     int
+	char     int
+	do       int
+	double   int
+	extern   int
+	float    int
+	inline   int
+	long     int
+	register int
+	restrict int
+	short    int
+	signed   int
+	typedef  int
+	unsigned int
+	void     int
+	volatile int
+	while    int
+}
+
+fn test_struct_levels() {
+	mut c := C{}
+	assert c.nums.len == 0
+	c.nums << 3
+	assert c.nums.len == 1
+	assert c.nums[0] == 3
+	c.nums[0] = 4
+	assert c.nums[0] == 4
+	c.b.a.val = 34
+	assert c.b.a.val == 34
+	c.b.a.nums = [0].repeat(0)
+	c.b.a.nums << 0
+	c.b.a.nums << 2
+	assert c.b.a.nums.len == 2
+	assert c.b.a.nums[0] == 0
+	assert c.b.a.nums[1] == 2
+	c.b.a.nums [0] = 7
+	assert c.b.a.nums[0] == 7
+	c.aarr << A{val:8}
+	assert c.aarr.len == 1
+	assert c.aarr[0].val == 8
+	c.num = 20
+	assert c.num == 20
+	c.aarr[0].val  = 10
+	assert c.aarr[0].val == 10
+}
+
+fn test_struct_str() {
+	u := User{'Bob', 30}
+	println(u)  // make sure the struct is printable
+	// assert u.str() == '{name:"Bob", age:30}'  // TODO
+}
+
+fn test_at() {
+	foo := Foo{ @type: 'test' }
+	println(foo.@type)
+}
+
+fn test_reserved_keywords() {
+	//Make sure we can initialize them correctly using full syntax.
+	rk_holder := ReservedKeywords{0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3}
+	//Test a few as it'll take too long to test all. If it's initialized
+	//correctly, other fields are also probably valid.
+	assert rk_holder.unix == 5
+	assert rk_holder.while == 3
+
+	rk_holder2 := ReservedKeywords{inline: 9, volatile: 11}
+	//Make sure partial initialization works too.
+	assert rk_holder2.inline == 9
+	assert rk_holder2.volatile == 11
+	assert rk_holder2.while == 0 //Zero value as not specified.
+}
+
+struct User2 {
+mut:
+	name string
+}	
+
+fn test_mutable_fields() {
+	mut u := User2{}
+	u.name = 'Peter'
+	assert u.name == 'Peter'
+}