node docs: Simplify and fix node docs.
node docs: Simplify and fix node docs.

This is a first pass at fixing node docs.  This commit eliminates
some text that is either obsolete or just overly confusing, and
it fixes some of the code samples to reflect how the API has
evolved in the last couple years.  We also prominently tell
you how to run the tests.

zulip/zulip,timabbott/zulip,rht/zulip,tommyip/zulip,brainwane/zulip,timabbott/zulip,shubhamdhama/zulip,andersk/zulip,showell/zulip,jackrzhang/zulip,kou/zulip,brainwane/zulip,kou/zulip,synicalsyntax/zulip,eeshangarg/zulip,rht/zulip,andersk/zulip,synicalsyntax/zulip,synicalsyntax/zulip,shubhamdhama/zulip,brainwane/zulip,punchagan/zulip,zulip/zulip,eeshangarg/zulip,synicalsyntax/zulip,jackrzhang/zulip,rht/zulip,punchagan/zulip,jackrzhang/zulip,zulip/zulip,shubhamdhama/zulip,tommyip/zulip,rht/zulip,showell/zulip,hackerkid/zulip,showell/zulip,rht/zulip,jackrzhang/zulip,kou/zulip,timabbott/zulip,dhcrzf/zulip,timabbott/zulip,shubhamdhama/zulip,dhcrzf/zulip,hackerkid/zulip,rishig/zulip,dhcrzf/zulip,eeshangarg/zulip,dhcrzf/zulip,tommyip/zulip,rishig/zulip,punchagan/zulip,punchagan/zulip,showell/zulip,timabbott/zulip,andersk/zulip,jackrzhang/zulip,timabbott/zulip,punchagan/zulip,jackrzhang/zulip,zulip/zulip,brainwane/zulip,eeshangarg/zulip,dhcrzf/zulip,tommyip/zulip,jackrzhang/zulip,andersk/zulip,synicalsyntax/zulip,shubhamdhama/zulip,synicalsyntax/zulip,kou/zulip,shubhamdhama/zulip,hackerkid/zulip,showell/zulip,tommyip/zulip,shubhamdhama/zulip,andersk/zulip,brainwane/zulip,tommyip/zulip,zulip/zulip,kou/zulip,brainwane/zulip,eeshangarg/zulip,eeshangarg/zulip,tommyip/zulip,hackerkid/zulip,punchagan/zulip,rht/zulip,kou/zulip,andersk/zulip,synicalsyntax/zulip,rishig/zulip,kou/zulip,rishig/zulip,hackerkid/zulip,timabbott/zulip,showell/zulip,showell/zulip,rishig/zulip,rishig/zulip,zulip/zulip,punchagan/zulip,rht/zulip,eeshangarg/zulip,andersk/zulip,rishig/zulip,dhcrzf/zulip,hackerkid/zulip,dhcrzf/zulip,hackerkid/zulip,zulip/zulip,brainwane/zulip