Reduce number of allocations for rendering elements and attributes (#265

)

This change does some optimizations to reduce the number of memory heap
allocations.

Also:
- Checks for `io.StringWriter` and uses that if available.
- Pre-allocates byte slices for commonly used strings.
- Fixed the benchmarks to not count `strings.Builder` allocations.

These are the benchmark results from before the changes (with the
benchmark fix):

```
go test -bench . -benchmem ./...
goos: darwin
goarch: arm64
pkg: maragu.dev/gomponents
cpu: Apple M3 Max
BenchmarkAttr/boolean_attributes-16         	25371446	        46.81 ns/op	      40 B/op	       3 allocs/op
BenchmarkAttr/name-value_attributes-16      	13534495	        88.24 ns/op	      72 B/op	       4 allocs/op
BenchmarkEl/normal_elements-16              	14068998	        86.28 ns/op	      48 B/op	       5 allocs/op
PASS
ok  	maragu.dev/gomponents	4.894s
PASS
ok  	maragu.dev/gomponents/components	0.163s
goos: darwin
goarch: arm64
pkg: maragu.dev/gomponents/html
cpu: Apple M3 Max
BenchmarkLargeHTMLDocument-16    	     526	   2092062 ns/op	 2950444 B/op	   90031 allocs/op
PASS
ok  	maragu.dev/gomponents/html	1.463s
PASS
ok  	maragu.dev/gomponents/http	0.168s
?   	maragu.dev/gomponents/internal/assert	[no test files]
PASS
ok  	maragu.dev/gomponents/internal/import	0.135s
```

After:

```
go test -bench . -benchmem ./...
goos: darwin
goarch: arm64
pkg: maragu.dev/gomponents
cpu: Apple M3 Max
BenchmarkAttr/boolean_attributes-16         	51947022	        19.75 ns/op	       8 B/op	       1 allocs/op
BenchmarkAttr/name-value_attributes-16      	18138727	        64.87 ns/op	      24 B/op	       2 allocs/op
BenchmarkEl/normal_elements-16              	21048692	        55.48 ns/op	      24 B/op	       2 allocs/op
PASS
ok  	maragu.dev/gomponents	3.687s
PASS
ok  	maragu.dev/gomponents/components	0.158s
goos: darwin
goarch: arm64
pkg: maragu.dev/gomponents/html
cpu: Apple M3 Max
BenchmarkLargeHTMLDocument-16    	     714	   1535017 ns/op	 2630426 B/op	   40028 allocs/op
PASS
ok  	maragu.dev/gomponents/html	1.398s
PASS
ok  	maragu.dev/gomponents/http	0.171s
?   	maragu.dev/gomponents/internal/assert	[no test files]
PASS
ok  	maragu.dev/gomponents/internal/import	0.137s
```

Benchmark large document and run in CI (#246)

Fixes #229

Release v1 (#226)

v1.0.0-beta1 gave no problems with my other gomponents libraries, that
of others, and some of my large projects, so releasing v1!

No more breaking changes! 😁

Remove mention of SVG package in doc comments

Remove SVG package (#214)

Because the added value of having this was very small, and I don't want
to confuse people about what's properly supported, I've removed the SVG
package. As #196 showed, there can easily be conflicts between HTML and
SVG, and the rendering isn't really set up for anything else than HTML.

It's still easy to create SVG elements: `html.SVG` exists in this repo,
and the rest is often just a string that can be included using `g.Raw`.

Fixes #206

Use go workspace in example app (#211)

Make Groups renderable (#181)

This change makes the result of `Group` renderable directly, instead of
panicking, with the important caveat that root-level attributes are
_ignored_. I don't think this will give problems in practice, as the
main use case for rendering `Group` is basically to return root-level
elements to the client using something like HTMX.

I tried adding a `Fragment`, but it was weird and confusing having two
functions (`Group` and `Fragment`) do essentially the same thing, the
only difference being whether the argument was a slice of `Node`s or
varargs.

Fixes #162

Add links to godoc (#183)

Also add an example for `http.Adapt`.

Fixes #182

Add LabelAttr and List attributes (#175)

Fixes #168 and fixes #169.

Fix wrong codecov (#166)

We don't need coverage for the example code and internal testing
helpers.