Specification:
1. An avx file is a text file describing alignments between multiple sequences. We denote the sequences by s_1,s_2,...,s_k.
2. The file is divided into blocks. Each block represents a single multiple alignment between any r of the sequences (2 <= r <= k). A block begins with identifiers for each sequence. The identifiers are of fasta style, namely they consist of lines beginning with the ">" symbol. The ">" is followed by a pair of numbers in brackets [a,b] designating the beginning and ending position in the sequence for this alignment block and then is followed by either a + or a - to indicated the strand which had alignment. Following this there is a regular text expression identifying the sequence.
For example, a block could begin:
> [10,100] + human region
> [2,150] - mouse region
> [3,1729] + dog region
3. The identifiers for a block are followed by the multiple alignment, showing the sequence characters with a "-" for gaps. For example:
ACGTGA---AGTGA
-CGAGATT-AATGA
ACGA--TTAAC--A