[feat] Generate URL of wget download script using ESGF RESTful API

[hongyuanjia]

Pull request overview

• Fixes #69
• Add a wget parameter with default value being FALSE in EsgfQuery$url(). Examples have been given in the method docs to show how to download the script.
• Also fix quite a few typos in documentation

[codecov-commenter]

Codecov Report

Merging #74 (b82215b) into master (cc62c23) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #74   +/-   ##
=======================================
  Coverage   99.80%   99.80%           
=======================================
  Files           8        8           
  Lines        2005     2007    +2     
=======================================
+ Hits         2001     2003    +2     
  Misses          4        4           

Impacted Files	Coverage Δ
R/dict.R	99.75% <ø> (ø)
R/esgf.R	100.00% <ø> (ø)
R/utils.R	96.87% <ø> (ø)
R/morph.R	100.00% <100.00%> (ø)
R/netcdf.R	99.48% <100.00%> (ø)
R/query.R	100.00% <100.00%> (ø)

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