Attmap

Added
- `OrdAttMap` to create maps that preserve insertion order and otherwise behave like ordinary `AttMap`
- `get_data_lines` utility, supporting nice instance `repr`
- `is_custom_map` utility
Changed
- Better `repr` and `str` for all `attmap`-like types, rendering like YAML
- `__getitem__` syntax on `AttMapEcho` no longer exhibits echo behavior (only dot notation does.)
- Instance comparison is now much stricter, requiring exact type match. This reflects some of the type-specific value conversion and representation behavior.
- `PathExAttMap` is now `OrdPathExAttMap`, preserving item insertion order
- `AttMapEcho` preserves item insertion order

Changed
- Removed `pandas` dependency
- Made hooks for omission of specific keys instance methods

Added
- Hook for omission of key(s) from instance comparison
- Documentation

Added
- Add `to_map` method to convert `Mapping` values to basic type

Changed
- What was `PepAttMap` is now `PathExAttMap`.

Added
- `PepAttMap` attempts expansion of text value as a path, using available environment variables
Changed
- `AttMap` now derives from `PepAttMap` rather than ordinary `AttMap`