v1.9

Update the 1.x branch to match the functions of seq 2.x

* seq.el (seq-some, seq-find, seq-contains): New and renamed functions.
* test/seq.el-test.el: Update the tests.
* README.md: Add/update the documentation of the new functions.

Update seq.el to v1.8

* seq.el: Update to version 1.8.
* test/seq.el-test.el (test-seq-let): Update to version
1.8.