Extract sycamore crate into multiple crates

[lukechu10]

New crates include:

• sycamore-core for core Sycamore functionality. This crate should provide backend-agnostic APIs. The web backend should also be included by default as that is by-far the most common use case for sycamore (at least for now).
• sycamore-web that adds a few web specific APIs and the web backend.

The sycamore crate should always re-export sycamore-core and re-export sycamore-web when a "web" feature is enabled (should it be enabled by default?)

This also updates the builder API to use free functions (i.e. div() instead of h(div)) and decouples it from html backends.
The builder API is also included by default and the builder feature is removed.

[codecov]

Codecov Report

Merging #416 (56b66f1) into master (3b3e39e) will decrease coverage by 0.02%.
The diff coverage is 47.84%.

@@            Coverage Diff             @@
##           master     #416      +/-   ##
==========================================
- Coverage   64.97%   64.95%   -0.03%     
==========================================
  Files          49       52       +3     
  Lines        8080     8289     +209     
==========================================
+ Hits         5250     5384     +134     
- Misses       2830     2905      +75     

Impacted Files	Coverage Δ
packages/sycamore-core/src/generic_node.rs	100.00% <ø> (ø)
packages/sycamore-core/src/view.rs	75.53% <ø> (ø)
packages/sycamore-macro/src/component/mod.rs	96.01% <ø> (ø)
packages/sycamore-macro/src/view/parse.rs	96.80% <ø> (ø)
packages/sycamore-reactive/src/lib.rs	96.40% <ø> (ø)
packages/sycamore-router-macro/src/route.rs	89.42% <ø> (ø)
packages/sycamore-router/src/lib.rs	96.77% <ø> (ø)
packages/sycamore-web/src/dom_node.rs	0.00% <0.00%> (ø)
packages/sycamore-web/src/hydrate.rs	0.00% <ø> (ø)
packages/sycamore-web/src/hydrate_node.rs	0.00% <ø> (ø)
... and 20 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3b3e39e...56b66f1. Read the comment docs.

[github-actions]

Finished dev [unoptimized + debuginfo] target(s) in 0.06s
 Running `/home/runner/work/sycamore/sycamore/sycamore/target/debug/bench-diff ../../../../js-framework-benchmark/webdriver-ts/results.json`

Benchmark Report

• wasm-bindgen: the performance goal
• baseline: performance of sycamore-baseline (typically latest master)
• update: performance of sycamore (typically recent changes)
• diff: measures the improvement of update over the baseline

@@                           Performance Diff                           @@

##                          | wasm-bindgen | baseline |  update |  diff ##
##########################################################################
+ 01_run1k                  |       164.34 |   217.27 |  209.24 |   -3.69%
+ 02_replace1k              |       174.51 |   229.27 |  221.38 |   -3.44%
+ 03_update10th1k_x16       |       410.64 |   446.42 |  401.27 |  -10.11%
  04_select1k               |        45.79 |    67.83 |   69.22 |   +2.04%
  05_swap1k                 |       101.45 |   101.10 |   99.51 |   -1.58%
  06_remove-one-1k          |        34.79 |    37.88 |   37.43 |   -1.17%
+ 07_create10k              |      2058.07 |  2971.82 | 2809.54 |   -5.46%
  08_create1k-after1k_x2    |       427.35 |   498.49 |  491.65 |   -1.37%
+ 09_clear1k_x8             |       111.90 |   152.18 |  139.93 |   -8.05%
  21_ready-memory           |         1.47 |     1.44 |    1.44 |   -0.05%
+ 22_run-memory             |         1.35 |     1.68 |    1.62 |   -3.67%
  23_update5-memory         |         1.35 |     1.65 |    1.64 |   -0.27%
  24_run5-memory            |         1.68 |     1.85 |    1.85 |   +0.11%
  25_run-clear-memory       |         1.41 |     1.28 |    1.27 |   -0.53%
  31_startup-ci             |      1862.63 |  2032.30 | 2032.73 |   +0.02%
  32_startup-bt             |        21.31 |    47.28 |   47.18 |   -0.23%
- 33_startup-mainthreadcost |       331.44 |   345.56 |  380.91 |  +10.23%
  34_startup-totalbytes     |       189.16 |   283.39 |  282.46 |   -0.33%

Workflow: 2335454036
Adding new commits will generate a new report