Add some additional scenarios to Excel append tests:
- Non-A1 start
- Name duplication
- Hitting another range
# Important Notes
Also fixed a warning in the Image library.
More and more often I need a way to only recover a specific type of a dataflow error (in a similar manner as with panics). So the API for `Error.catch` has been amended to more closely resemble `Panic.catch`, allowing to handle only specific types of dataflow errors, passing others through unchanged. The default is `Any`, meaning all errors are caught by default, and the behaviour of `x.catch` remains unchanged.
A semi-manual s/this/self appied to the whole standard library.
Related to https://www.pivotaltracker.com/story/show/182328601
In the compiler promoted to use constants instead of hardcoded
`this`/`self` whenever possible.
# Important Notes
The PR **does not** require explicit `self` parameter declaration for methods as this part
of the design is still under consideration.
Auto-generate all builtin methods for builtin `File` type from method signatures.
Similarly, for `ManagedResource` and `Warning`.
Additionally, support for specializations for overloaded and non-overloaded methods is added.
Coverage can be tracked by the number of hard-coded builtin classes that are now deleted.
## Important notes
Notice how `type File` now lacks `prim_file` field and we were able to get rid off all of those
propagating method calls without writing a single builtin node class.
Similarly `ManagedResource` and `Warning` are now builtins and `Prim_Warnings` stub is now gone.
- Added Encoding type
- Added `Text.bytes`, `Text.from_bytes` with Encoding support
- Renamed `File.read` to `File.read_text`
- Renamed `File.write` to `File.write_text`
- Added Encoding support to `File.read_text` and `File.write_text`
- Added warnings to invalid encodings
