Drop WithContext methods

[magiconair]

As announced in v0.3.0 we will drop all WithContext() methods in v0.5.0 and require that the non-WithContext() methods require a context.Context

func (c *Client) Read(...) {...}
func (c *Client) ReadWithContext(ctx context.Context, ...) { ... }

will become

func (c *Client) Read(ctx context.Context, ...) { ... }

[magiconair]

This needs a rebase after v0.3.1