Mecha

Feature
* Remove providers, add global ctx again, and tweak generate_tree ([`e03969e`](https://github.com/mcbeet/mecha/commit/e03969efe4d177f7e2ae2b67e4e78f047478ef01))

Feature
* Add scripting sandbox ([`ae343d2`](https://github.com/mcbeet/mecha/commit/ae343d262525880dd63ff4305183d201646cc88a))
* Expose generate utilities ([`9ef34c6`](https://github.com/mcbeet/mecha/commit/9ef34c6e53f01ba6e1d58bfcdc2d54eea3a12d85))

Fix
* Store builtin names on the runtime ([`bc747e0`](https://github.com/mcbeet/mecha/commit/bc747e0cf17d20897c5fb6769750185b5024f6e1))

Fix
* Off-by-one line mapping ([`7fcd2da`](https://github.com/mcbeet/mecha/commit/7fcd2dab6b602fd000f7efc5a28a63089145c00c))
* Import regular python modules through helper ([`6ff1de3`](https://github.com/mcbeet/mecha/commit/6ff1de302c09dba220ae450c7904d8a8f4a5a1ce))

Feature
* Provide ctx and current_path through runtime import ([`c62167a`](https://github.com/mcbeet/mecha/commit/c62167aa7f9fa543ea6eeaa5646adf3125bcc923))

Fix
* Allow optional separator for imported names ([`e07af65`](https://github.com/mcbeet/mecha/commit/e07af658fd9efdda919ec6c2de412a73fd9be823))

Fix
* Proper execution order for interpolation with nested root ([`2bab7b2`](https://github.com/mcbeet/mecha/commit/2bab7b2d1ba06924b2770dc6dd4fed664a10972a))
* Report unserializable nodes and remove MessageReferenceSerializer ([`137022d`](https://github.com/mcbeet/mecha/commit/137022dff37fef73a8e7ce8cdc90876264e14d23))

Fix
* Invalid interpolation for keys in selector arguments and block states ([`3e8999f`](https://github.com/mcbeet/mecha/commit/3e8999f67651dd67e67c59ffd9a166b0373288ef))