[DOCS] Fix ML post_data docs (elastic/x-pack-elasticsearch#2689)
[DOCS] Fix ML post_data docs (elastic/x-pack-elasticsearch#2689)

It was pointed out in
https://github.com/elastic/elasticsearch-net/pull/2856#discussion_r142830656
that our post_data docs incorrectly say that reset_start and reset_end are
body parameters.  In fact they are query parameters.

There were also a number of other errors and ommissions on this page that I
have attempted to correct.

Original commit: elastic/x-pack-elasticsearch@c83decacc709560e797e9d3ea805e16ce7b1362a

gfyoung/elasticsearch,GlenRSmith/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,scorpionvicky/elasticsearch,GlenRSmith/elasticsearch,scorpionvicky/elasticsearch,HonzaKral/elasticsearch,uschindler/elasticsearch,HonzaKral/elasticsearch,gfyoung/elasticsearch,gingerwizard/elasticsearch,scorpionvicky/elasticsearch,coding0011/elasticsearch,nknize/elasticsearch,gfyoung/elasticsearch,gfyoung/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,scorpionvicky/elasticsearch,coding0011/elasticsearch,gingerwizard/elasticsearch,coding0011/elasticsearch,nknize/elasticsearch,nknize/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,coding0011/elasticsearch,uschindler/elasticsearch,robin13/elasticsearch,coding0011/elasticsearch,scorpionvicky/elasticsearch,HonzaKral/elasticsearch,HonzaKral/elasticsearch,robin13/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,gfyoung/elasticsearch,uschindler/elasticsearch,gingerwizard/elasticsearch