Updated dependencies

• updated and pinned dependencies
• #36
• #38

nth partial and log

• New functions for the n-th partial derivative partial_nth and partial_iter
• Added ln for natural logarithm. We have now log2, log10, log, and ln where the latter 2 are identical.
• [BREAKING] e is an additional way to write Euler's constant in addition to E.
• eval_relaxed does not complain if more variables are passed than parsed.

τ

[Breaking] τ = 2π is now a constant and cannot be used as variable anymore.

One owning expression type

• BREAKING, removed OwnedFlatEx and made FlatEx owning since parsing time differences are negligible.
• Fixed if/else operators for value.
• BREAKING, from_str is no longer a method of Express. Instead, FlatEx implements FromStr.
• BREAKING, partial is now a feature to compute partial derivatives that is not activated by default.
• BREAKING, fixed de-serialization of traits with custom operand/number literals. A new trait MatchLiteral can be used to implement custom operands in a serializable way.

Hotfix operator next to binary operator

The case where a operator is on the left of a binary operator lead to a panic and is now handled as error.

Faster Parsing

• Parsing is signifantly faster, almost factor 2
• Breaking ExError::from_str -> ExError::new
• Breaking field prio of Operator is now i64 instead of i32.
• Uncompiled expressions accessible via public interface
• Display shows the original string

Value type

• introduced value type feature that allows to combine booleans, floats, and ints in one expression
• Breaking, renamed DefaultOpsFactory to FloatOpsFactory
• Added interface for pre-compiled regexes for number literals

Clone for data types sufficient

For the "numeric" data type it is sufficient to implement Clone. Before, Copy was required.

Check partial out of bounds

• Added a check if the demanded partial derivative is valid. Before, it would just return 0, since the expression obviously does not depend on it.
• Exposed number of variables to the public interface.

Unicode

Unicode input strings are now supported.