created alternative data loader function .

[00krishna]

Created a new faster data loader function load_ipums_extract_v2(). This function is faster than the original load_ipums_extract() function. The signature is the same. To test the file, you can use code like.

    ddi = parse_ddi("testdata/cps_00157.xml")
    datafile = "testdata/cps_00157.dat"
    
    @btime df = load_ipums_extract(ddi, datafile)
    @btime df2 = load_ipums_extract_v2(ddi, datafile)

[00krishna]

READY FOR REVIEW.

Okay, I cleaned up a few additional things.

• removed the old version of the loader functions.
• removed unneeded dependency
• removed unneeded test cases
• formatted the ddi_parsers.jl to make it look better.

[TheCedarPrince]

LGTM -- merging! Thanks so much @00krishna!