Add Result<?> DSLContext.fetchFromTXT() to allow for loading results that were exported using Result.format()

[lukaseder]

This is a consequence of a discussion with Aaron Digulla on the user-group:
https://groups.google.com/d/topic/jooq-user/OQzuxbqk-w8/discussion

Loading results from TXT could be particularly useful for unit testing through a MockFileDatabase: #2208. In particular, this method should support two modes:

• H2 mode
• Format mode

The H2 mode contains results formatted in this way:

F1  F2  F3 is a bit more complex
--- --  ----------------------------
1   2   and a string containing data
1.1 x   another string

...where the dash line specifies the column widths

The Format mode contains results formatted in this way:

+---+--+
|F1 |F2|
+---+--+
|1  |2 |
|1.1|x |
+---+--+

... where the first line specifies the column widths, and columns are padded with one space