some files seem to have the format header preceded by large amounts of junk but this appears to be valid for chrome and acrobat reader. this change ups the amount of nonsense to be read prior to the version header.
also makes parsing of the version header culture invariant which may be related to #85.
if the previous cross-reference location points to an offset outside the file size we skip it.
also makes cid font factory more resilient by skipping missing descriptors.
an %%eof for a pdf file may appear further back than the last 1024 bytes. this change doubles the search range. it also handles an empty differences array being defined for a font encoding.
we also remove the old approach to dependency injection from the code since we are now favouring static classes where possible.
the 3 font types mentioned are moved to the new fonts project, any referenced types are moved to the core project. most truetype classes are made public #8.
to make the project more useful and expose more usable classes we're rearchitecting in the following way. code used to read fonts from external file formats like truetype, adobe font metrics (afm) and adobe type 1 fonts are moving to a new project which doesn't reference most of the pdf logic. the shared logic is moving to a new flat-structured project called core. this is a sort-of onion type architecture, with core being the... core, fonts being the next layer of the onion, pdfpig itself the next. this will then support additional libraries/projects as outer layers of the onion as well as releasing standalone version of the font library as pdfbox does with fontbox.
package license url is deprecated in favour of package license expression but nuget doesn't seem to support expressions properly for published packages yet so we'll keep the deprecated url for the time being. having both url and expression causes the build to fail.
small obvious performance improvements for file header passing and getting the encoding information using the existing reverse name to code map.
previously if the cross reference did not exist at exactly the provided offset we'd immediately throw, now we assume we can read a few more tokens to find the xref table or stream start. this won't work in the case where the provided offset is past the start of the table or nowhere near the table but in those cases there's not much we can do. there's some more work to do to provide a fallback xref parser which finds the xref tables and streams using a brute-force scan of the whole document.
