Improve linking for internal headers

[chussong]

This pull request makes the following changes:

• Most struct declarations were of the form typedef struct name_s { /* data fields */ } name_t, but some were typedef'd anonymously (without name_s): typedef struct { /* data fields */ } name_t. This made it impossible to forward declare them. I have added the name_s part to all headers which omitted it.

• A seemingly random selection of the internal headers had the extern "C" required for linking with C++, but many did not have it; also, most of the internal headers containing extern "C" used a style that differed from the style used in the public API headers, and some had extraneous semicolons which caused compiler warnings. I have added the directive to all internal headers and unified the style with that of the public API headers.

• ps_lattice_internal.h required pocketsphinx_internal.h but did not include it, so it would not work unless pocketsphinx_internal.h was included first. I have added the missing #include directive.

[nshmyrev]

Looks great, thank you!