Rename functions in iodata.formats submodules (?)

[tovrstra]

We use the same names in iodata.api as in the submodules of iodata.formats, e.g. iodata.formats.fcidump. For example, they both have load_one and dump_one. Yet, these functions have different APIs, which may be confusing. When the names are the same, one may easily assume they are completely compatible.

An example of this type of confusion can be found in #367.

We may clarify this be renaming the functions in the formats modules, to emphasize their difference in arguments. For example, load_one_fmt, dump_one_fmt, etc. (If we want this, we'd better do it before 1.0.0.)