Renamed types (removed `toml` prefix).
Refactoring API hidding values type.
Functions allows to retrieve and add an abstract value from a table,
to go from an abstract value to a concrete one,
and from a concrete one to an abstract one.
Cleaning repo.
Pprint module is not part of library, (part of tests at most).
Added opam file.
Moved type into TomlInternal module so it can be exposed in
different library modules but not exported as part of the
library.
Old Pprint module restored as TomlInternal.Dump module.
Removed [string_of_] prefix from Dump functions. Added Equal module
for table/value/array equality testing.
Fixed tests using new Toml interface. Remove helper_test.ml
which was not relevant any ore since it was testing the old interface.
Introduced Key module in order to abstract the type of table keys.
Fixed #7 gh issue.
[#5] Add printer.

Add a Toml.Printer module to make it possible to serialize a TOML structure to
string, as a valid TOML document.
Stylistic improvements.
[#5] Removes the last uses of the Printf module in print_* functions.

This incidentally improves the display of floating numbers, and makes the
print_* functions more homogenous.
[#5] Removes wrong call to Key.of_string.
Merge pull request #8 from Emm/v2_printer

V2 printer
Used 2 spaces indent instead of 4 spaces.
Fixed [all_values_are_table].
Simplyfied string printing.
Removed / factorized some small portions of code.
[#9] Makes the key type abstract.
[#9] Don't copy Key's signature.