Expose prepared statements

[tvandinther]

Closes #25

This MR implements an interface to expose prepared statements. The internals are also changed to support this new feature.

Public interface changes are present in this MR.

Parameter binding implementation
Bound parameters are held internally in C# and are bound late when the statement is sent for execution. Resetting the statement currently creates a new prepared statement. A change to the bindings code needs to be made to make this both performant and to prevent new bindings from being made.

[tvandinther]

Wondering if I revert this to commit 5401452

The current implementation isn't ideal.

However, need to solve the issue in 5401452 where getting the first row of a queried statement after it was reset returns a row with a null pointer which creates a column type array with an enum value of 0 which is invalid. Seems like there is some kind of cursor reset somewhere?

[tvandinther]

Waiting for fix to C bindings to be merged upstream tursodatabase/libsql#1713

[tvandinther]

Upstream fix has been merged. This branch requires an update to the revision of libsql being built to include it.

[tvandinther]

Update: This feature requires some extra FFI bindings as defined in this branch/fork: https://github.com/tvandinther/libsql/tree/add-missing-statement-functions

It appears that libsql_stmt_columns is the last function to be correctly implemented for this feature to be ready.