Allow configuration of typographical replacements, e.g. smart quotes

If you're living in a non-UTF-8 character set, then you can configure what quotes are smartly changed.
If my regexes are messing things up, you can also turn this off with smart_quotes: false
Also updated docs.

This closes #50

lib/squib/project_template/config.yml

@@ -25,3 +25,16 @@
 # Use a SVG cairo back end, instead of an in-memory buffer
 # backend: :memory # default
 # backend: :svg    # can create scalable pdfs, but rendering done at the printer level is not as good as Cairo.
+
+# Configure what text markup uses replace characters
+# Below are the defaults
+# lsquote: "\u2018" #note that Yaml wants double quotes here to use escape chars
+# rsquote: "\u2019"
+# ldquote: "\u201C"
+# rdquote: "\u201D"
+# em_dash: "\u2014"
+# en_dash: "\u2013"
+# ellipsis: "\u2026"
+
+# We can also disallow smart quotes and only allow explicit replacements with ``LaTeX-style'' quotes.
+# smart_quotes: false