Smarter escaping of Markdown

[jindrahelcl]

There are compromises to be made.

• In this version, backslashes, asterisks, and underscores are always escaped.
• Things that have special meaning on the beginning of a line are escaped if they are at the start of a line and in the proper context.
• pipes are escaped only if they are found inside tables
• square brackets are only escaped if they are inside a link text.

everything else remains unescaped, which also means that there might be some accidental markdown meaning, but this may also match the original intention (like an accidental table or such)