Escaped pipe character in markdown docs in tables

[michalbundyra]

Resolves #65

It requires https://github.com/zendframework/zf-mkdoc-theme/pull/30 to be released first.

Basically we always escape pipes in cells in markdown notation and after generating HTML we 'unescape' them in html files (because html generators is not doing that).

I've tested it and it works correctly. If anyone like to test it you can do the following steps:

1. Clone repo and checkout branch with the fix:

   # git clone https://github.com/webimpress/zend-navigation.git
   # cd zend-navigation
   # git checkout hotfix/65

2. Install dependencies:

   # pip install --user mkdocs
   # pip install --user pymdown-extensions

3. Download updated zf-mkdoc-theme from my branch and unzip it:

   # wget https://github.com/webimpress/zf-mkdoc-theme/archive/hotfix/pipes-in-tables.zip
   # unzip pipes-in-tables.zip
   # mv zf-mkdoc-theme-hotfix-pipes-in-tables/ zf-mkdoc-theme

4. Build the docs from md files:

   # zf-mkdoc-theme/build.sh

The docs should be build in zend-navigation/doc/html/ directory.

/cc @froschdesign

[michalbundyra]

@froschdesign zf-mkdoc-theme is now merged and released as 0.5.3 so this PR can be now merged :)

[weierophinney]

Thanks, @webimpress