Update some links and references

[larsbarring]

In the HTML version of the Conventions document the "keywords" are shown as expected in the reference list, but not in the PDF version. See this example:

HTML:

black_small_square [NetCDF][ NetCDF Software Package](http://www.unidata.ucar.edu/netcdf/index.html) . UNIDATA Program Center of the University Corporation for Atmospheric Research

PDF:

black_small_square [] [NetCDF Software Package](http://www.unidata.ucar.edu/netcdf/index.html) . UNIDATA Program Center of the University Corporation for Atmospheric Research .

---

Another small thing that I just came across: The link in the [Snyder] reference item should be updated to read
"https://pubs.er.usgs.gov/publication/pp1395" (or is this a separate issue + PR?)

PS:

... and a simple typo in the reference item just above:

[SCH02] C Schaer, D Leuenberger, and O Fuhrer. 2002. “ A new terrain-following vertical coordiante formulation for atmospheric prediction models ”. Monthly Weather Review . 130 . 2459-2480

[JonathanGregory]

Thanks for this defect issue of last September, @larsbarring. I see that the appearance of the keywords and little black squares have been corrected in the bibliography of the pdf of the current working version but the Synder link and the typo you found have not been fixed. I have therefore prepared PR 441 to make these corrections. I will merge it myself now (hoping I've got it right), because far more than three weeks have passed since you raised the issue. Jonathan

[larsbarring]

Following the comment by @JonathanGregory that

... I note that the Snyder map projection document [...] has a DOI, which would be more future-proof, viz https://doi.org/10.3133/pp1395.

I am reopening this issue and will shortly create a new PR to replace the current link with the DOI.

[JonathanGregory]

Thanks, Lars. I think we can regard this as resolving the same defect as before, so I'll merge it now.