C API C_1.1.2

Performance improvements

• tsk_tree_seek is now much faster at seeking to arbitrary points along
  the sequence from the null tree (@molpopgen, #2661).

Features

• The struct tsk_treeseq_t now has the variables min_time and max_time,
  which are the minimum and maximum among the node times and mutation times,
  respectively. min_time and max_time can be accessed using the functions
  tsk_treeseq_get_min_time and tsk_treeseq_get_max_time, respectively.
  (@szhan, #2612, #2271)

• Add the TSK_SIMPLIFY_NO_FILTER_NODES option to simplify to allow unreferenced
  nodes be kept in the output (@jeromekelleher, @hyanwong,
  #2606, #2619).

• Add the TSK_SIMPLIFY_NO_UPDATE_SAMPLE_FLAGS option to simplify which ensures
  no node sample flags are changed to allow calling code to manage sample status.
  (@jeromekelleher, #2662, #2663).

• Guarantee that unfiltered tables are not written to unnecessarily
  during simplify (@jeromekelleher #2619).

• Add x_table_keep_rows methods to provide efficient in-place table subsetting
  (@jeromekelleher, #2700).

• Add tsk_tree_seek_index function