Pare down the number of exported functions

[ddsjoberg]

Only export functions intended for users (i.e. no helpers, etc).

Potential functions that are more internal than for use by a typical user

• legendopts()
• align_plots()
• get_tableone()
• get_summary()
• the_lhs()
• get_risktable() - I think it's fine to export this one eventually, but in its current state the output is in a format for internal use: not for use by users, e.g. returns a data frame with columns like y_value, which makes sense for how it's used internally in add_risktable(). But not useful for users.
• All the summarize_*() functions