Asana tasks cleanup

See https://app.asana.com/0/11724913287040/14477880045173

- improve README.md
- use `@label@` to label shortcuts, objects and other things in `graph_objs_meta.py`
- table of content resides `graph_objs_meta-toc.py`
add glossary, val type and contributing info
improve README.md aesthetics
A few quick-hit Asana tasks

- check https://app.asana.com/0/11724913287040/14477880045188
- check https://app.asana.com/0/11724913287040/14477880045194
- check https://app.asana.com/0/11724913287040/14477880045192
- check https://app.asana.com/0/11724913287040/14477880045224
Check Asana task https://app.asana.com/0/11724913287040/14477880045220

- drops 'thickness' in Line
- drops 'drange', 'r0' in Axis
- drops 'bardir' in Layout
- better description for 'autorange' in Axis
- better description for 'autosize' in Layout
- correct typo in 'angularaxis' , 'radialaxis'
Check Asana task #2

- set 'z' to required in Heatmap and Contour https://app.asana.com/0/11724913287040/14477880045186
- fill in 'traceref' description https://app.asana.com/0/11724913287040/14477880045210
- correctly describe current state of 'domain' in 'angularaxis' and 'radialaxis' https://app.asana.com/0/11724913287040/14477880045222
- add info to README.md about artifacts
Check Asana task #3

- describe 'boxpoints': 'suspectedoutliers' https://app.asana.com/0/11724913287040/14477880045206
- better describe Box
- add 'outliercolor' in Marker
- add 'outliercolor' and 'outlierwidth' in Line
Check Asana task #3

- better describe 'sizeref' and 'sizemode' https://app.asana.com/0/11724913287040/14477880045214
- better describe 'size'
Check Asana task #5

- better describe 'smoothing' and 'spline' in Line
- drop 'axtype', 'axtype', 'tag', 'ref' in Annotation
- better describe 'x/yanchor', 'x/yref', 'align', 'x' and 'y' in Annotation and Legend
- better describe 'separators' and 'hidesources' in Layout
- drop 'labeloffset'
- a few typos here and there
typo in Annotation 'textangle', to pass circle
Check Asana task 6

- add 'colorscale' to all 2d trace objects (leave 'scl' as artifact )https://app.asana.com/0/7838292824434/14477880045212/f
- add 'reversescale' to all 2d trace objects (leave 'reverscl' as artifact)
- add 'cauto', 'cmin', 'cmax' in Marker (to fine-tune Scatter color maps)
- set 'orientation' to 'plot_info' https://app.asana.com/0/7838292824434/14477880045190/f
- set 'nticks' and 'tick0' to 'styple https://app.asana.com/0/7838292824434/14477880045202/f
fix typo, add 'cmax' to Marker
Check Asana #7 (Lucky 7)

- set 'range' to 'plot_info' https://app.asana.com/0/7838292824434/14477880045200/f
- set 'nbinx' and 'nbiny' to 'plot_info' https://app.asana.com/0/7838292824434/14477880045196/f
- update README.md with info about 'type':'plot_info'
-
drop 'scl' and 'reversescl' from 2d trace objects
put parts of README.md in CONTRIBUTING.md
README.md and CONTRIBUTING.mb aesthetics
README.md aesthetics (2)
README.md aesthetics (3)
Finally making sense of 'type' 'plot_info' & 'style'

- modify 'type' for numberous keys.
- better describes a few keys in XAxis and YAxis
- drop 'traceref' in ErrorX and ErrorY (couldn't settle on 'type')
fix typo to pass circle