feat(#37): head tail movement support + deprecate previous API's

[armed]

fixes #37
Here is config example:

    ["E"] = {
      paredit.api.move_to_next_element_tail,
      "Jump to next element tail",
      -- by default all keybindings are dot repeatable
      repeatable = false,
      mode = { "n", "x", "o", "v" },
    },
    ["W"] = {
      paredit.api.move_to_next_element_head,
      "Jump to next element head",
      repeatable = false,
      mode = { "n", "x", "o", "v" },
    },

    ["B"] = {
      paredit.api.move_to_prev_element_head,
      "Jump to previous element head",
      repeatable = false,
      mode = { "n", "x", "o", "v" },
    },
    ["gE"] = {
      paredit.api.move_to_prev_element_tail,
      "Jump to previous element tail",
      repeatable = false,
      mode = { "n", "x", "o", "v" },
    },

• paredit.api.move_to_next_element is deprecated in favour of paredit.api.move_to_next_element_tail
• paredit.api.move_to_prev_element is deprecated in favour of paredit.api.move_to_prev_element_head

[julienvincent]

Sweet!