[#1] Load configuration from "cobalt.json" stored in the root direcotry for Cobalt.
[#2] Load all templates and store them in a value typed as "Generator".
[#3] Create a temporary directory on initialization of a value typed "OutputDirectory".
[#2] Load contents and iterate their names by using "Directory".
[#2] Read the meta data from the front matter.
[#2] Read the main content from the markdown-formatted text.
[#2] Generator.generate(*Content) executes templates but doesn't write the result of executing to files.
[#2] Write generated HTMLs into the temporary directory and remove them after flushing.
[#2] Remove a debug message.
[#2] A value typed as "*Content" has config and they are passed to "Generator.generate(*Content)".
[#2] Create sub directories in the temporary directory for generated HTML files.
[#3] Flush generated HTML files and static files to the output directory.
[#4] Print the descripton of error to stderr.
[#4] Fix the lack of generation of error value.
[#4] Print error messages with "cobalt: " as their prefix.
[#5] Refactor a little.
[#5] Merge branch 'feature/prototyping' into develop