add config.toml support for different fonts

Author: graevy

assets/sass/override.scss

@@ -2,7 +2,7 @@
 $body-bg: {{ if .Param "style.backgroundColor" }}{{ .Param "style.backgroundColor"}}{{ else }}#f8f9fa{{ end }};
 $body-color: {{ if .Param "style.fontColor" }}{{ .Param "style.fontColor"}}{{ else }}#212529{{ end }};
 $home-image-border-color: {{ if .Param "style.homeImageBorderColor" }}{{ .Param "style.homeImageBorderColor"}}{{ else }}#ffffff{{ end }};
-$font-family-base: "Helvetica Neue", Arial, sans-serif;
+$font-family-base: {{ if .Param "style.fontFamilyBase"}}{{ .Param "style.fontFamilyBase"}},{{end}}"Helvetica Neue", Arial, sans-serif;
 $font-size-base: 0.95rem;
 @import "../../node_modules/bootstrap/scss/bootstrap";